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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source to the Rust file `liballoc/btree/map.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>map.rs.html -- source</title><link rel="stylesheet" type="text/css" href="../../../normalize.css"><link rel="stylesheet" type="text/css" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../../dark.css"><link rel="stylesheet" type="text/css" href="../../../light.css" id="themeStyle"><script src="../../../storage.js"></script><link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"></head><body class="rustdoc source"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">&#9776;</div><a href='../../../alloc/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><input class="search-input" name="search" autocomplete="off" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><a id="settings-menu" href="../../../settings.html"><img src="../../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><pre class="line-numbers"><span id="1">   1</span>
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</pre><pre class="rust ">
<span class="comment">// Copyright 2015 The Rust Project Developers. See the COPYRIGHT</span>
<span class="comment">// file at the top-level directory of this distribution and at</span>
<span class="comment">// http://rust-lang.org/COPYRIGHT.</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 &lt;LICENSE-APACHE or</span>
<span class="comment">// http://www.apache.org/licenses/LICENSE-2.0&gt; or the MIT license</span>
<span class="comment">// &lt;LICENSE-MIT or http://opensource.org/licenses/MIT&gt;, at your</span>
<span class="comment">// option. This file may not be copied, modified, or distributed</span>
<span class="comment">// except according to those terms.</span>

<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">cmp</span>::<span class="ident">Ordering</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">fmt</span>::<span class="ident">Debug</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">hash</span>::{<span class="ident">Hash</span>, <span class="ident">Hasher</span>};
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">iter</span>::{<span class="ident">FromIterator</span>, <span class="ident">Peekable</span>, <span class="ident">FusedIterator</span>};
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">marker</span>::<span class="ident">PhantomData</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">ops</span>::<span class="ident">Bound</span>::{<span class="ident">Excluded</span>, <span class="ident">Included</span>, <span class="ident">Unbounded</span>};
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">ops</span>::<span class="ident">Index</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">ops</span>::<span class="ident">RangeBounds</span>;
<span class="kw">use</span> <span class="ident">core</span>::{<span class="ident">fmt</span>, <span class="ident">intrinsics</span>, <span class="ident">mem</span>, <span class="ident">ptr</span>};

<span class="kw">use</span> <span class="ident">borrow</span>::<span class="ident">Borrow</span>;

<span class="kw">use</span> <span class="kw">super</span>::<span class="ident">node</span>::{<span class="self">self</span>, <span class="ident">Handle</span>, <span class="ident">NodeRef</span>, <span class="ident">marker</span>};
<span class="kw">use</span> <span class="kw">super</span>::<span class="ident">search</span>;

<span class="kw">use</span> <span class="kw">super</span>::<span class="ident">node</span>::<span class="ident">InsertResult</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="kw">super</span>::<span class="ident">node</span>::<span class="ident">ForceResult</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="kw">super</span>::<span class="ident">search</span>::<span class="ident">SearchResult</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="self">self</span>::<span class="ident">UnderflowResult</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="self">self</span>::<span class="ident">Entry</span>::<span class="kw-2">*</span>;

<span class="doccomment">/// A map based on a B-Tree.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// B-Trees represent a fundamental compromise between cache-efficiency and actually minimizing</span>
<span class="doccomment">/// the amount of work performed in a search. In theory, a binary search tree (BST) is the optimal</span>
<span class="doccomment">/// choice for a sorted map, as a perfectly balanced BST performs the theoretical minimum amount of</span>
<span class="doccomment">/// comparisons necessary to find an element (log&lt;sub&gt;2&lt;/sub&gt;n). However, in practice the way this</span>
<span class="doccomment">/// is done is *very* inefficient for modern computer architectures. In particular, every element</span>
<span class="doccomment">/// is stored in its own individually heap-allocated node. This means that every single insertion</span>
<span class="doccomment">/// triggers a heap-allocation, and every single comparison should be a cache-miss. Since these</span>
<span class="doccomment">/// are both notably expensive things to do in practice, we are forced to at very least reconsider</span>
<span class="doccomment">/// the BST strategy.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A B-Tree instead makes each node contain B-1 to 2B-1 elements in a contiguous array. By doing</span>
<span class="doccomment">/// this, we reduce the number of allocations by a factor of B, and improve cache efficiency in</span>
<span class="doccomment">/// searches. However, this does mean that searches will have to do *more* comparisons on average.</span>
<span class="doccomment">/// The precise number of comparisons depends on the node search strategy used. For optimal cache</span>
<span class="doccomment">/// efficiency, one could search the nodes linearly. For optimal comparisons, one could search</span>
<span class="doccomment">/// the node using binary search. As a compromise, one could also perform a linear search</span>
<span class="doccomment">/// that initially only checks every i&lt;sup&gt;th&lt;/sup&gt; element for some choice of i.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Currently, our implementation simply performs naive linear search. This provides excellent</span>
<span class="doccomment">/// performance on *small* nodes of elements which are cheap to compare. However in the future we</span>
<span class="doccomment">/// would like to further explore choosing the optimal search strategy based on the choice of B,</span>
<span class="doccomment">/// and possibly other factors. Using linear search, searching for a random element is expected</span>
<span class="doccomment">/// to take O(B log&lt;sub&gt;B&lt;/sub&gt;n) comparisons, which is generally worse than a BST. In practice,</span>
<span class="doccomment">/// however, performance is excellent.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// It is a logic error for a key to be modified in such a way that the key&#39;s ordering relative to</span>
<span class="doccomment">/// any other key, as determined by the [`Ord`] trait, changes while it is in the map. This is</span>
<span class="doccomment">/// normally only possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Ord`]: ../../std/cmp/trait.Ord.html</span>
<span class="doccomment">/// [`Cell`]: ../../std/cell/struct.Cell.html</span>
<span class="doccomment">/// [`RefCell`]: ../../std/cell/struct.RefCell.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::collections::BTreeMap;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // type inference lets us omit an explicit type signature (which</span>
<span class="doccomment">/// // would be `BTreeMap&lt;&amp;str, &amp;str&gt;` in this example).</span>
<span class="doccomment">/// let mut movie_reviews = BTreeMap::new();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // review some movies.</span>
<span class="doccomment">/// movie_reviews.insert(&quot;Office Space&quot;,       &quot;Deals with real issues in the workplace.&quot;);</span>
<span class="doccomment">/// movie_reviews.insert(&quot;Pulp Fiction&quot;,       &quot;Masterpiece.&quot;);</span>
<span class="doccomment">/// movie_reviews.insert(&quot;The Godfather&quot;,      &quot;Very enjoyable.&quot;);</span>
<span class="doccomment">/// movie_reviews.insert(&quot;The Blues Brothers&quot;, &quot;Eye lyked it alot.&quot;);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // check for a specific one.</span>
<span class="doccomment">/// if !movie_reviews.contains_key(&quot;Les Misérables&quot;) {</span>
<span class="doccomment">///     println!(&quot;We&#39;ve got {} reviews, but Les Misérables ain&#39;t one.&quot;,</span>
<span class="doccomment">///              movie_reviews.len());</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // oops, this review has a lot of spelling mistakes, let&#39;s delete it.</span>
<span class="doccomment">/// movie_reviews.remove(&quot;The Blues Brothers&quot;);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // look up the values associated with some keys.</span>
<span class="doccomment">/// let to_find = [&quot;Up!&quot;, &quot;Office Space&quot;];</span>
<span class="doccomment">/// for book in &amp;to_find {</span>
<span class="doccomment">///     match movie_reviews.get(book) {</span>
<span class="doccomment">///        Some(review) =&gt; println!(&quot;{}: {}&quot;, book, review),</span>
<span class="doccomment">///        None =&gt; println!(&quot;{} is unreviewed.&quot;, book)</span>
<span class="doccomment">///     }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // iterate over everything.</span>
<span class="doccomment">/// for (movie, review) in &amp;movie_reviews {</span>
<span class="doccomment">///     println!(&quot;{}: \&quot;{}\&quot;&quot;, movie, review);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `BTreeMap` also implements an [`Entry API`](#method.entry), which allows</span>
<span class="doccomment">/// for more complex methods of getting, setting, updating and removing keys and</span>
<span class="doccomment">/// their values:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::collections::BTreeMap;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // type inference lets us omit an explicit type signature (which</span>
<span class="doccomment">/// // would be `BTreeMap&lt;&amp;str, u8&gt;` in this example).</span>
<span class="doccomment">/// let mut player_stats = BTreeMap::new();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn random_stat_buff() -&gt; u8 {</span>
<span class="doccomment">///     // could actually return some random value here - let&#39;s just return</span>
<span class="doccomment">///     // some fixed value for now</span>
<span class="doccomment">///     42</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // insert a key only if it doesn&#39;t already exist</span>
<span class="doccomment">/// player_stats.entry(&quot;health&quot;).or_insert(100);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // insert a key using a function that provides a new value only if it</span>
<span class="doccomment">/// // doesn&#39;t already exist</span>
<span class="doccomment">/// player_stats.entry(&quot;defence&quot;).or_insert_with(random_stat_buff);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // update a key, guarding against the key possibly not being set</span>
<span class="doccomment">/// let stat = player_stats.entry(&quot;attack&quot;).or_insert(100);</span>
<span class="doccomment">/// *stat += random_stat_buff();</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="ident">root</span>: <span class="ident">node</span>::<span class="ident">Root</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>,
    <span class="ident">length</span>: <span class="ident">usize</span>,
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_drop&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.7.0&quot;</span>)]</span>
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op">&lt;</span><span class="attribute">#[<span class="ident">may_dangle</span>]</span> <span class="ident">K</span>, <span class="attribute">#[<span class="ident">may_dangle</span>]</span> <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) {
        <span class="kw">unsafe</span> {
            <span class="ident">drop</span>(<span class="ident">ptr</span>::<span class="ident">read</span>(<span class="self">self</span>).<span class="ident">into_iter</span>());
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">Clone</span>, <span class="ident">V</span>: <span class="ident">Clone</span><span class="op">&gt;</span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="kw">fn</span> <span class="ident">clone_subtree</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">Clone</span>, <span class="ident">V</span>: <span class="ident">Clone</span><span class="op">&gt;</span>(<span class="ident">node</span>: <span class="ident">node</span>::<span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Immut</span>,
                                                                 <span class="ident">K</span>,
                                                                 <span class="ident">V</span>,
                                                                 <span class="ident">marker</span>::<span class="ident">LeafOrInternal</span><span class="op">&gt;</span>)
                                             <span class="op">-&gt;</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {

            <span class="kw">match</span> <span class="ident">node</span>.<span class="ident">force</span>() {
                <span class="ident">Leaf</span>(<span class="ident">leaf</span>) <span class="op">=&gt;</span> {
                    <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">out_tree</span> <span class="op">=</span> <span class="ident">BTreeMap</span> {
                        <span class="ident">root</span>: <span class="ident">node</span>::<span class="ident">Root</span>::<span class="ident">new_leaf</span>(),
                        <span class="ident">length</span>: <span class="number">0</span>,
                    };

                    {
                        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">out_node</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">out_tree</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>().<span class="ident">force</span>() {
                            <span class="ident">Leaf</span>(<span class="ident">leaf</span>) <span class="op">=&gt;</span> <span class="ident">leaf</span>,
                            <span class="ident">Internal</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> <span class="macro">unreachable</span><span class="macro">!</span>(),
                        };

                        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">in_edge</span> <span class="op">=</span> <span class="ident">leaf</span>.<span class="ident">first_edge</span>();
                        <span class="kw">while</span> <span class="kw">let</span> <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=</span> <span class="ident">in_edge</span>.<span class="ident">right_kv</span>() {
                            <span class="kw">let</span> (<span class="ident">k</span>, <span class="ident">v</span>) <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">into_kv</span>();
                            <span class="ident">in_edge</span> <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">right_edge</span>();

                            <span class="ident">out_node</span>.<span class="ident">push</span>(<span class="ident">k</span>.<span class="ident">clone</span>(), <span class="ident">v</span>.<span class="ident">clone</span>());
                            <span class="ident">out_tree</span>.<span class="ident">length</span> <span class="op">+=</span> <span class="number">1</span>;
                        }
                    }

                    <span class="ident">out_tree</span>
                }
                <span class="ident">Internal</span>(<span class="ident">internal</span>) <span class="op">=&gt;</span> {
                    <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">out_tree</span> <span class="op">=</span> <span class="ident">clone_subtree</span>(<span class="ident">internal</span>.<span class="ident">first_edge</span>().<span class="ident">descend</span>());

                    {
                        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">out_node</span> <span class="op">=</span> <span class="ident">out_tree</span>.<span class="ident">root</span>.<span class="ident">push_level</span>();
                        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">in_edge</span> <span class="op">=</span> <span class="ident">internal</span>.<span class="ident">first_edge</span>();
                        <span class="kw">while</span> <span class="kw">let</span> <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=</span> <span class="ident">in_edge</span>.<span class="ident">right_kv</span>() {
                            <span class="kw">let</span> (<span class="ident">k</span>, <span class="ident">v</span>) <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">into_kv</span>();
                            <span class="ident">in_edge</span> <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">right_edge</span>();

                            <span class="kw">let</span> <span class="ident">k</span> <span class="op">=</span> (<span class="kw-2">*</span><span class="ident">k</span>).<span class="ident">clone</span>();
                            <span class="kw">let</span> <span class="ident">v</span> <span class="op">=</span> (<span class="kw-2">*</span><span class="ident">v</span>).<span class="ident">clone</span>();
                            <span class="kw">let</span> <span class="ident">subtree</span> <span class="op">=</span> <span class="ident">clone_subtree</span>(<span class="ident">in_edge</span>.<span class="ident">descend</span>());

                            <span class="comment">// We can&#39;t destructure subtree directly</span>
                            <span class="comment">// because BTreeMap implements Drop</span>
                            <span class="kw">let</span> (<span class="ident">subroot</span>, <span class="ident">sublength</span>) <span class="op">=</span> <span class="kw">unsafe</span> {
                                <span class="kw">let</span> <span class="ident">root</span> <span class="op">=</span> <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="ident">subtree</span>.<span class="ident">root</span>);
                                <span class="kw">let</span> <span class="ident">length</span> <span class="op">=</span> <span class="ident">subtree</span>.<span class="ident">length</span>;
                                <span class="ident">mem</span>::<span class="ident">forget</span>(<span class="ident">subtree</span>);
                                (<span class="ident">root</span>, <span class="ident">length</span>)
                            };

                            <span class="ident">out_node</span>.<span class="ident">push</span>(<span class="ident">k</span>, <span class="ident">v</span>, <span class="ident">subroot</span>);
                            <span class="ident">out_tree</span>.<span class="ident">length</span> <span class="op">+=</span> <span class="number">1</span> <span class="op">+</span> <span class="ident">sublength</span>;
                        }
                    }

                    <span class="ident">out_tree</span>
                }
            }
        }

        <span class="ident">clone_subtree</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>())
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">Q</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span> <span class="kw">super</span>::<span class="ident">Recover</span><span class="op">&lt;</span><span class="ident">Q</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, ()<span class="op">&gt;</span>
    <span class="kw">where</span> <span class="ident">K</span>: <span class="ident">Borrow</span><span class="op">&lt;</span><span class="ident">Q</span><span class="op">&gt;</span> <span class="op">+</span> <span class="ident">Ord</span>,
          <span class="ident">Q</span>: <span class="ident">Ord</span>
{
    <span class="kw">type</span> <span class="ident">Key</span> <span class="op">=</span> <span class="ident">K</span>;

    <span class="kw">fn</span> <span class="ident">get</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">key</span>: <span class="kw-2">&amp;</span><span class="ident">Q</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="ident">K</span><span class="op">&gt;</span> {
        <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_tree</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>(), <span class="ident">key</span>) {
            <span class="ident">Found</span>(<span class="ident">handle</span>) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>(<span class="ident">handle</span>.<span class="ident">into_kv</span>().<span class="number">0</span>),
            <span class="ident">GoDown</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
        }
    }

    <span class="kw">fn</span> <span class="ident">take</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">key</span>: <span class="kw-2">&amp;</span><span class="ident">Q</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">K</span><span class="op">&gt;</span> {
        <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_tree</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>(), <span class="ident">key</span>) {
            <span class="ident">Found</span>(<span class="ident">handle</span>) <span class="op">=&gt;</span> {
                <span class="prelude-val">Some</span>(<span class="ident">OccupiedEntry</span> {
                         <span class="ident">handle</span>,
                         <span class="ident">length</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">length</span>,
                         <span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
                     }
                     .<span class="ident">remove_kv</span>()
                     .<span class="number">0</span>)
            }
            <span class="ident">GoDown</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
        }
    }

    <span class="kw">fn</span> <span class="ident">replace</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">key</span>: <span class="ident">K</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">K</span><span class="op">&gt;</span> {
        <span class="self">self</span>.<span class="ident">ensure_root_is_owned</span>();
        <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_tree</span>::<span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Mut</span>, <span class="ident">K</span>, (), <span class="ident">K</span><span class="op">&gt;</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>(), <span class="kw-2">&amp;</span><span class="ident">key</span>) {
            <span class="ident">Found</span>(<span class="ident">handle</span>) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>(<span class="ident">mem</span>::<span class="ident">replace</span>(<span class="ident">handle</span>.<span class="ident">into_kv_mut</span>().<span class="number">0</span>, <span class="ident">key</span>)),
            <span class="ident">GoDown</span>(<span class="ident">handle</span>) <span class="op">=&gt;</span> {
                <span class="ident">VacantEntry</span> {
                    <span class="ident">key</span>,
                    <span class="ident">handle</span>,
                    <span class="ident">length</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">length</span>,
                    <span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
                }
                .<span class="ident">insert</span>(());
                <span class="prelude-val">None</span>
            }
        }
    }
}

<span class="doccomment">/// An iterator over the entries of a `BTreeMap`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This `struct` is created by the [`iter`] method on [`BTreeMap`]. See its</span>
<span class="doccomment">/// documentation for more.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`iter`]: struct.BTreeMap.html#method.iter</span>
<span class="doccomment">/// [`BTreeMap`]: struct.BTreeMap.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    <span class="ident">range</span>: <span class="ident">Range</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>,
    <span class="ident">length</span>: <span class="ident">usize</span>,
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;collection_debug&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Debug</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Debug</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="ident">f</span>.<span class="ident">debug_list</span>().<span class="ident">entries</span>(<span class="self">self</span>.<span class="ident">clone</span>()).<span class="ident">finish</span>()
    }
}

<span class="doccomment">/// A mutable iterator over the entries of a `BTreeMap`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This `struct` is created by the [`iter_mut`] method on [`BTreeMap`]. See its</span>
<span class="doccomment">/// documentation for more.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`iter_mut`]: struct.BTreeMap.html#method.iter_mut</span>
<span class="doccomment">/// [`BTreeMap`]: struct.BTreeMap.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">IterMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    <span class="ident">range</span>: <span class="ident">RangeMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>,
    <span class="ident">length</span>: <span class="ident">usize</span>,
}

<span class="doccomment">/// An owning iterator over the entries of a `BTreeMap`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This `struct` is created by the [`into_iter`] method on [`BTreeMap`][`BTreeMap`]</span>
<span class="doccomment">/// (provided by the `IntoIterator` trait). See its documentation for more.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`into_iter`]: struct.BTreeMap.html#method.into_iter</span>
<span class="doccomment">/// [`BTreeMap`]: struct.BTreeMap.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="ident">front</span>: <span class="ident">Handle</span><span class="op">&lt;</span><span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Owned</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Leaf</span><span class="op">&gt;</span>, <span class="ident">marker</span>::<span class="ident">Edge</span><span class="op">&gt;</span>,
    <span class="ident">back</span>: <span class="ident">Handle</span><span class="op">&lt;</span><span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Owned</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Leaf</span><span class="op">&gt;</span>, <span class="ident">marker</span>::<span class="ident">Edge</span><span class="op">&gt;</span>,
    <span class="ident">length</span>: <span class="ident">usize</span>,
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;collection_debug&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">fmt</span>::<span class="ident">Debug</span>, <span class="ident">V</span>: <span class="ident">fmt</span>::<span class="ident">Debug</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="kw">let</span> <span class="ident">range</span> <span class="op">=</span> <span class="ident">Range</span> {
            <span class="ident">front</span>: <span class="self">self</span>.<span class="ident">front</span>.<span class="ident">reborrow</span>(),
            <span class="ident">back</span>: <span class="self">self</span>.<span class="ident">back</span>.<span class="ident">reborrow</span>(),
        };
        <span class="ident">f</span>.<span class="ident">debug_list</span>().<span class="ident">entries</span>(<span class="ident">range</span>).<span class="ident">finish</span>()
    }
}

<span class="doccomment">/// An iterator over the keys of a `BTreeMap`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This `struct` is created by the [`keys`] method on [`BTreeMap`]. See its</span>
<span class="doccomment">/// documentation for more.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`keys`]: struct.BTreeMap.html#method.keys</span>
<span class="doccomment">/// [`BTreeMap`]: struct.BTreeMap.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Keys</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    <span class="ident">inner</span>: <span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>,
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;collection_debug&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Debug</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">Keys</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="ident">f</span>.<span class="ident">debug_list</span>().<span class="ident">entries</span>(<span class="self">self</span>.<span class="ident">clone</span>()).<span class="ident">finish</span>()
    }
}

<span class="doccomment">/// An iterator over the values of a `BTreeMap`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This `struct` is created by the [`values`] method on [`BTreeMap`]. See its</span>
<span class="doccomment">/// documentation for more.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`values`]: struct.BTreeMap.html#method.values</span>
<span class="doccomment">/// [`BTreeMap`]: struct.BTreeMap.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Values</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    <span class="ident">inner</span>: <span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>,
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;collection_debug&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Debug</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">Values</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="ident">f</span>.<span class="ident">debug_list</span>().<span class="ident">entries</span>(<span class="self">self</span>.<span class="ident">clone</span>()).<span class="ident">finish</span>()
    }
}

<span class="doccomment">/// A mutable iterator over the values of a `BTreeMap`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This `struct` is created by the [`values_mut`] method on [`BTreeMap`]. See its</span>
<span class="doccomment">/// documentation for more.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`values_mut`]: struct.BTreeMap.html#method.values_mut</span>
<span class="doccomment">/// [`BTreeMap`]: struct.BTreeMap.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;map_values_mut&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.10.0&quot;</span>)]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ValuesMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    <span class="ident">inner</span>: <span class="ident">IterMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>,
}

<span class="doccomment">/// An iterator over a sub-range of entries in a `BTreeMap`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This `struct` is created by the [`range`] method on [`BTreeMap`]. See its</span>
<span class="doccomment">/// documentation for more.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`range`]: struct.BTreeMap.html#method.range</span>
<span class="doccomment">/// [`BTreeMap`]: struct.BTreeMap.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_range&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Range</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    <span class="ident">front</span>: <span class="ident">Handle</span><span class="op">&lt;</span><span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Immut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Leaf</span><span class="op">&gt;</span>, <span class="ident">marker</span>::<span class="ident">Edge</span><span class="op">&gt;</span>,
    <span class="ident">back</span>: <span class="ident">Handle</span><span class="op">&lt;</span><span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Immut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Leaf</span><span class="op">&gt;</span>, <span class="ident">marker</span>::<span class="ident">Edge</span><span class="op">&gt;</span>,
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;collection_debug&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Debug</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Debug</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">Range</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="ident">f</span>.<span class="ident">debug_list</span>().<span class="ident">entries</span>(<span class="self">self</span>.<span class="ident">clone</span>()).<span class="ident">finish</span>()
    }
}

<span class="doccomment">/// A mutable iterator over a sub-range of entries in a `BTreeMap`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This `struct` is created by the [`range_mut`] method on [`BTreeMap`]. See its</span>
<span class="doccomment">/// documentation for more.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`range_mut`]: struct.BTreeMap.html#method.range_mut</span>
<span class="doccomment">/// [`BTreeMap`]: struct.BTreeMap.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_range&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">RangeMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    <span class="ident">front</span>: <span class="ident">Handle</span><span class="op">&lt;</span><span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Mut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Leaf</span><span class="op">&gt;</span>, <span class="ident">marker</span>::<span class="ident">Edge</span><span class="op">&gt;</span>,
    <span class="ident">back</span>: <span class="ident">Handle</span><span class="op">&lt;</span><span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Mut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Leaf</span><span class="op">&gt;</span>, <span class="ident">marker</span>::<span class="ident">Edge</span><span class="op">&gt;</span>,

    <span class="comment">// Be invariant in `K` and `V`</span>
    <span class="ident">_marker</span>: <span class="ident">PhantomData</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> (<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;</span>,
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;collection_debug&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Debug</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Debug</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">RangeMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="kw">let</span> <span class="ident">range</span> <span class="op">=</span> <span class="ident">Range</span> {
            <span class="ident">front</span>: <span class="self">self</span>.<span class="ident">front</span>.<span class="ident">reborrow</span>(),
            <span class="ident">back</span>: <span class="self">self</span>.<span class="ident">back</span>.<span class="ident">reborrow</span>(),
        };
        <span class="ident">f</span>.<span class="ident">debug_list</span>().<span class="ident">entries</span>(<span class="ident">range</span>).<span class="ident">finish</span>()
    }
}

<span class="doccomment">/// A view into a single entry in a map, which may either be vacant or occupied.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This `enum` is constructed from the [`entry`] method on [`BTreeMap`].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`BTreeMap`]: struct.BTreeMap.html</span>
<span class="doccomment">/// [`entry`]: struct.BTreeMap.html#method.entry</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">Entry</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    <span class="doccomment">/// A vacant entry.</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="ident">Vacant</span>(<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
           <span class="ident">VacantEntry</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>),

    <span class="doccomment">/// An occupied entry.</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="ident">Occupied</span>(<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
             <span class="ident">OccupiedEntry</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>),
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span><span class="op">=</span> <span class="string">&quot;debug_btree_map&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.12.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">Debug</span> <span class="op">+</span> <span class="ident">Ord</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">Debug</span><span class="op">&gt;</span> <span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">Entry</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
            <span class="ident">Vacant</span>(<span class="kw-2">ref</span> <span class="ident">v</span>) <span class="op">=&gt;</span> <span class="ident">f</span>.<span class="ident">debug_tuple</span>(<span class="string">&quot;Entry&quot;</span>)
                              .<span class="ident">field</span>(<span class="ident">v</span>)
                              .<span class="ident">finish</span>(),
            <span class="ident">Occupied</span>(<span class="kw-2">ref</span> <span class="ident">o</span>) <span class="op">=&gt;</span> <span class="ident">f</span>.<span class="ident">debug_tuple</span>(<span class="string">&quot;Entry&quot;</span>)
                                .<span class="ident">field</span>(<span class="ident">o</span>)
                                .<span class="ident">finish</span>(),
        }
    }
}

<span class="doccomment">/// A view into a vacant entry in a `BTreeMap`.</span>
<span class="doccomment">/// It is part of the [`Entry`] enum.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Entry`]: enum.Entry.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">VacantEntry</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    <span class="ident">key</span>: <span class="ident">K</span>,
    <span class="ident">handle</span>: <span class="ident">Handle</span><span class="op">&lt;</span><span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Mut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Leaf</span><span class="op">&gt;</span>, <span class="ident">marker</span>::<span class="ident">Edge</span><span class="op">&gt;</span>,
    <span class="ident">length</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">usize</span>,

    <span class="comment">// Be invariant in `K` and `V`</span>
    <span class="ident">_marker</span>: <span class="ident">PhantomData</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> (<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;</span>,
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span><span class="op">=</span> <span class="string">&quot;debug_btree_map&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.12.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">Debug</span> <span class="op">+</span> <span class="ident">Ord</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">VacantEntry</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="ident">f</span>.<span class="ident">debug_tuple</span>(<span class="string">&quot;VacantEntry&quot;</span>)
         .<span class="ident">field</span>(<span class="self">self</span>.<span class="ident">key</span>())
         .<span class="ident">finish</span>()
    }
}

<span class="doccomment">/// A view into an occupied entry in a `BTreeMap`.</span>
<span class="doccomment">/// It is part of the [`Entry`] enum.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Entry`]: enum.Entry.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">OccupiedEntry</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    <span class="ident">handle</span>: <span class="ident">Handle</span><span class="op">&lt;</span><span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Mut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">LeafOrInternal</span><span class="op">&gt;</span>, <span class="ident">marker</span>::<span class="ident">KV</span><span class="op">&gt;</span>,

    <span class="ident">length</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">usize</span>,

    <span class="comment">// Be invariant in `K` and `V`</span>
    <span class="ident">_marker</span>: <span class="ident">PhantomData</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> (<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;</span>,
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span><span class="op">=</span> <span class="string">&quot;debug_btree_map&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.12.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">Debug</span> <span class="op">+</span> <span class="ident">Ord</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span> <span class="op">+</span> <span class="ident">Debug</span><span class="op">&gt;</span> <span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">OccupiedEntry</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">&quot;OccupiedEntry&quot;</span>)
         .<span class="ident">field</span>(<span class="string">&quot;key&quot;</span>, <span class="self">self</span>.<span class="ident">key</span>())
         .<span class="ident">field</span>(<span class="string">&quot;value&quot;</span>, <span class="self">self</span>.<span class="ident">get</span>())
         .<span class="ident">finish</span>()
    }
}

<span class="comment">// An iterator for merging two sorted sequences into one</span>
<span class="kw">struct</span> <span class="ident">MergeIter</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">I</span>: <span class="ident">Iterator</span><span class="op">&lt;</span><span class="ident">Item</span> <span class="op">=</span> (<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;&gt;</span> {
    <span class="ident">left</span>: <span class="ident">Peekable</span><span class="op">&lt;</span><span class="ident">I</span><span class="op">&gt;</span>,
    <span class="ident">right</span>: <span class="ident">Peekable</span><span class="op">&lt;</span><span class="ident">I</span><span class="op">&gt;</span>,
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">Ord</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="doccomment">/// Makes a new empty BTreeMap with a reasonable choice for B.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map = BTreeMap::new();</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// // entries can now be inserted into the empty map</span>
    <span class="doccomment">/// map.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-&gt;</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="ident">BTreeMap</span> {
            <span class="ident">root</span>: <span class="ident">node</span>::<span class="ident">Root</span>::<span class="ident">shared_empty_root</span>(),
            <span class="ident">length</span>: <span class="number">0</span>,
        }
    }

    <span class="doccomment">/// Clears the map, removing all values.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut a = BTreeMap::new();</span>
    <span class="doccomment">/// a.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">/// a.clear();</span>
    <span class="doccomment">/// assert!(a.is_empty());</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">clear</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) {
        <span class="kw-2">*</span><span class="self">self</span> <span class="op">=</span> <span class="ident">BTreeMap</span>::<span class="ident">new</span>();
    }

    <span class="doccomment">/// Returns a reference to the value corresponding to the key.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// The key may be any borrowed form of the map&#39;s key type, but the ordering</span>
    <span class="doccomment">/// on the borrowed form *must* match the ordering on the key type.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map = BTreeMap::new();</span>
    <span class="doccomment">/// map.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">/// assert_eq!(map.get(&amp;1), Some(&amp;&quot;a&quot;));</span>
    <span class="doccomment">/// assert_eq!(map.get(&amp;2), None);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get</span><span class="op">&lt;</span><span class="ident">Q</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">key</span>: <span class="kw-2">&amp;</span><span class="ident">Q</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="ident">V</span><span class="op">&gt;</span>
        <span class="kw">where</span> <span class="ident">K</span>: <span class="ident">Borrow</span><span class="op">&lt;</span><span class="ident">Q</span><span class="op">&gt;</span>,
              <span class="ident">Q</span>: <span class="ident">Ord</span>
    {
        <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_tree</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>(), <span class="ident">key</span>) {
            <span class="ident">Found</span>(<span class="ident">handle</span>) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>(<span class="ident">handle</span>.<span class="ident">into_kv</span>().<span class="number">1</span>),
            <span class="ident">GoDown</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
        }
    }

    <span class="doccomment">/// Returns the key-value pair corresponding to the supplied key.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// The supplied key may be any borrowed form of the map&#39;s key type, but the ordering</span>
    <span class="doccomment">/// on the borrowed form *must* match the ordering on the key type.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// #![feature(map_get_key_value)]</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map = BTreeMap::new();</span>
    <span class="doccomment">/// map.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">/// assert_eq!(map.get_key_value(&amp;1), Some((&amp;1, &amp;&quot;a&quot;)));</span>
    <span class="doccomment">/// assert_eq!(map.get_key_value(&amp;2), None);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;map_get_key_value&quot;</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">&quot;49347&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get_key_value</span><span class="op">&lt;</span><span class="ident">Q</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">k</span>: <span class="kw-2">&amp;</span><span class="ident">Q</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="kw-2">&amp;</span><span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="ident">V</span>)<span class="op">&gt;</span>
        <span class="kw">where</span> <span class="ident">K</span>: <span class="ident">Borrow</span><span class="op">&lt;</span><span class="ident">Q</span><span class="op">&gt;</span>,
              <span class="ident">Q</span>: <span class="ident">Ord</span>
    {
        <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_tree</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>(), <span class="ident">k</span>) {
            <span class="ident">Found</span>(<span class="ident">handle</span>) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>(<span class="ident">handle</span>.<span class="ident">into_kv</span>()),
            <span class="ident">GoDown</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
        }
    }

    <span class="doccomment">/// Returns `true` if the map contains a value for the specified key.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// The key may be any borrowed form of the map&#39;s key type, but the ordering</span>
    <span class="doccomment">/// on the borrowed form *must* match the ordering on the key type.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map = BTreeMap::new();</span>
    <span class="doccomment">/// map.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">/// assert_eq!(map.contains_key(&amp;1), true);</span>
    <span class="doccomment">/// assert_eq!(map.contains_key(&amp;2), false);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">contains_key</span><span class="op">&lt;</span><span class="ident">Q</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">key</span>: <span class="kw-2">&amp;</span><span class="ident">Q</span>) <span class="op">-&gt;</span> <span class="ident">bool</span>
        <span class="kw">where</span> <span class="ident">K</span>: <span class="ident">Borrow</span><span class="op">&lt;</span><span class="ident">Q</span><span class="op">&gt;</span>,
              <span class="ident">Q</span>: <span class="ident">Ord</span>
    {
        <span class="self">self</span>.<span class="ident">get</span>(<span class="ident">key</span>).<span class="ident">is_some</span>()
    }

    <span class="doccomment">/// Returns a mutable reference to the value corresponding to the key.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// The key may be any borrowed form of the map&#39;s key type, but the ordering</span>
    <span class="doccomment">/// on the borrowed form *must* match the ordering on the key type.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map = BTreeMap::new();</span>
    <span class="doccomment">/// map.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">/// if let Some(x) = map.get_mut(&amp;1) {</span>
    <span class="doccomment">///     *x = &quot;b&quot;;</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// assert_eq!(map[&amp;1], &quot;b&quot;);</span>
    <span class="doccomment">/// ```</span>
    <span class="comment">// See `get` for implementation notes, this is basically a copy-paste with mut&#39;s added</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get_mut</span><span class="op">&lt;</span><span class="ident">Q</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">key</span>: <span class="kw-2">&amp;</span><span class="ident">Q</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">V</span><span class="op">&gt;</span>
        <span class="kw">where</span> <span class="ident">K</span>: <span class="ident">Borrow</span><span class="op">&lt;</span><span class="ident">Q</span><span class="op">&gt;</span>,
              <span class="ident">Q</span>: <span class="ident">Ord</span>
    {
        <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_tree</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>(), <span class="ident">key</span>) {
            <span class="ident">Found</span>(<span class="ident">handle</span>) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>(<span class="ident">handle</span>.<span class="ident">into_kv_mut</span>().<span class="number">1</span>),
            <span class="ident">GoDown</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
        }
    }

    <span class="doccomment">/// Inserts a key-value pair into the map.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// If the map did not have this key present, `None` is returned.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// If the map did have this key present, the value is updated, and the old</span>
    <span class="doccomment">/// value is returned. The key is not updated, though; this matters for</span>
    <span class="doccomment">/// types that can be `==` without being identical. See the [module-level</span>
    <span class="doccomment">/// documentation] for more.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// [module-level documentation]: index.html#insert-and-complex-keys</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map = BTreeMap::new();</span>
    <span class="doccomment">/// assert_eq!(map.insert(37, &quot;a&quot;), None);</span>
    <span class="doccomment">/// assert_eq!(map.is_empty(), false);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// map.insert(37, &quot;b&quot;);</span>
    <span class="doccomment">/// assert_eq!(map.insert(37, &quot;c&quot;), Some(&quot;b&quot;));</span>
    <span class="doccomment">/// assert_eq!(map[&amp;37], &quot;c&quot;);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">insert</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">key</span>: <span class="ident">K</span>, <span class="ident">value</span>: <span class="ident">V</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">V</span><span class="op">&gt;</span> {
        <span class="kw">match</span> <span class="self">self</span>.<span class="ident">entry</span>(<span class="ident">key</span>) {
            <span class="ident">Occupied</span>(<span class="kw-2">mut</span> <span class="ident">entry</span>) <span class="op">=&gt;</span> <span class="prelude-val">Some</span>(<span class="ident">entry</span>.<span class="ident">insert</span>(<span class="ident">value</span>)),
            <span class="ident">Vacant</span>(<span class="ident">entry</span>) <span class="op">=&gt;</span> {
                <span class="ident">entry</span>.<span class="ident">insert</span>(<span class="ident">value</span>);
                <span class="prelude-val">None</span>
            }
        }
    }

    <span class="doccomment">/// Removes a key from the map, returning the value at the key if the key</span>
    <span class="doccomment">/// was previously in the map.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// The key may be any borrowed form of the map&#39;s key type, but the ordering</span>
    <span class="doccomment">/// on the borrowed form *must* match the ordering on the key type.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map = BTreeMap::new();</span>
    <span class="doccomment">/// map.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">/// assert_eq!(map.remove(&amp;1), Some(&quot;a&quot;));</span>
    <span class="doccomment">/// assert_eq!(map.remove(&amp;1), None);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">remove</span><span class="op">&lt;</span><span class="ident">Q</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">key</span>: <span class="kw-2">&amp;</span><span class="ident">Q</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">V</span><span class="op">&gt;</span>
        <span class="kw">where</span> <span class="ident">K</span>: <span class="ident">Borrow</span><span class="op">&lt;</span><span class="ident">Q</span><span class="op">&gt;</span>,
              <span class="ident">Q</span>: <span class="ident">Ord</span>
    {
        <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_tree</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>(), <span class="ident">key</span>) {
            <span class="ident">Found</span>(<span class="ident">handle</span>) <span class="op">=&gt;</span> {
                <span class="prelude-val">Some</span>(<span class="ident">OccupiedEntry</span> {
                         <span class="ident">handle</span>,
                         <span class="ident">length</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">length</span>,
                         <span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
                     }
                     .<span class="ident">remove</span>())
            }
            <span class="ident">GoDown</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> <span class="prelude-val">None</span>,
        }
    }

    <span class="doccomment">/// Moves all elements from `other` into `Self`, leaving `other` empty.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut a = BTreeMap::new();</span>
    <span class="doccomment">/// a.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">/// a.insert(2, &quot;b&quot;);</span>
    <span class="doccomment">/// a.insert(3, &quot;c&quot;);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut b = BTreeMap::new();</span>
    <span class="doccomment">/// b.insert(3, &quot;d&quot;);</span>
    <span class="doccomment">/// b.insert(4, &quot;e&quot;);</span>
    <span class="doccomment">/// b.insert(5, &quot;f&quot;);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// a.append(&amp;mut b);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(a.len(), 5);</span>
    <span class="doccomment">/// assert_eq!(b.len(), 0);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(a[&amp;1], &quot;a&quot;);</span>
    <span class="doccomment">/// assert_eq!(a[&amp;2], &quot;b&quot;);</span>
    <span class="doccomment">/// assert_eq!(a[&amp;3], &quot;d&quot;);</span>
    <span class="doccomment">/// assert_eq!(a[&amp;4], &quot;e&quot;);</span>
    <span class="doccomment">/// assert_eq!(a[&amp;5], &quot;f&quot;);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_append&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.11.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">append</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">Self</span>) {
        <span class="comment">// Do we have to append anything at all?</span>
        <span class="kw">if</span> <span class="ident">other</span>.<span class="ident">len</span>() <span class="op">==</span> <span class="number">0</span> {
            <span class="kw">return</span>;
        }

        <span class="comment">// We can just swap `self` and `other` if `self` is empty.</span>
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">len</span>() <span class="op">==</span> <span class="number">0</span> {
            <span class="ident">mem</span>::<span class="ident">swap</span>(<span class="self">self</span>, <span class="ident">other</span>);
            <span class="kw">return</span>;
        }

        <span class="comment">// First, we merge `self` and `other` into a sorted sequence in linear time.</span>
        <span class="kw">let</span> <span class="ident">self_iter</span> <span class="op">=</span> <span class="ident">mem</span>::<span class="ident">replace</span>(<span class="self">self</span>, <span class="ident">BTreeMap</span>::<span class="ident">new</span>()).<span class="ident">into_iter</span>();
        <span class="kw">let</span> <span class="ident">other_iter</span> <span class="op">=</span> <span class="ident">mem</span>::<span class="ident">replace</span>(<span class="ident">other</span>, <span class="ident">BTreeMap</span>::<span class="ident">new</span>()).<span class="ident">into_iter</span>();
        <span class="kw">let</span> <span class="ident">iter</span> <span class="op">=</span> <span class="ident">MergeIter</span> {
            <span class="ident">left</span>: <span class="ident">self_iter</span>.<span class="ident">peekable</span>(),
            <span class="ident">right</span>: <span class="ident">other_iter</span>.<span class="ident">peekable</span>(),
        };

        <span class="comment">// Second, we build a tree from the sorted sequence in linear time.</span>
        <span class="self">self</span>.<span class="ident">from_sorted_iter</span>(<span class="ident">iter</span>);
        <span class="self">self</span>.<span class="ident">fix_right_edge</span>();
    }

    <span class="doccomment">/// Constructs a double-ended iterator over a sub-range of elements in the map.</span>
    <span class="doccomment">/// The simplest way is to use the range syntax `min..max`, thus `range(min..max)` will</span>
    <span class="doccomment">/// yield elements from min (inclusive) to max (exclusive).</span>
    <span class="doccomment">/// The range may also be entered as `(Bound&lt;T&gt;, Bound&lt;T&gt;)`, so for example</span>
    <span class="doccomment">/// `range((Excluded(4), Included(10)))` will yield a left-exclusive, right-inclusive</span>
    <span class="doccomment">/// range from 4 to 10.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Panics</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Panics if range `start &gt; end`.</span>
    <span class="doccomment">/// Panics if range `start == end` and both bounds are `Excluded`.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">/// use std::ops::Bound::Included;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map = BTreeMap::new();</span>
    <span class="doccomment">/// map.insert(3, &quot;a&quot;);</span>
    <span class="doccomment">/// map.insert(5, &quot;b&quot;);</span>
    <span class="doccomment">/// map.insert(8, &quot;c&quot;);</span>
    <span class="doccomment">/// for (&amp;key, &amp;value) in map.range((Included(&amp;4), Included(&amp;8))) {</span>
    <span class="doccomment">///     println!(&quot;{}: {}&quot;, key, value);</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// assert_eq!(Some((&amp;5, &amp;&quot;b&quot;)), map.range(4..).next());</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_range&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">range</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span>, <span class="ident">R</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">range</span>: <span class="ident">R</span>) <span class="op">-&gt;</span> <span class="ident">Range</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>
        <span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Ord</span>, <span class="ident">K</span>: <span class="ident">Borrow</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>, <span class="ident">R</span>: <span class="ident">RangeBounds</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>
    {
        <span class="kw">let</span> <span class="ident">root1</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>();
        <span class="kw">let</span> <span class="ident">root2</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>();
        <span class="kw">let</span> (<span class="ident">f</span>, <span class="ident">b</span>) <span class="op">=</span> <span class="ident">range_search</span>(<span class="ident">root1</span>, <span class="ident">root2</span>, <span class="ident">range</span>);

        <span class="ident">Range</span> { <span class="ident">front</span>: <span class="ident">f</span>, <span class="ident">back</span>: <span class="ident">b</span>}
    }

    <span class="doccomment">/// Constructs a mutable double-ended iterator over a sub-range of elements in the map.</span>
    <span class="doccomment">/// The simplest way is to use the range syntax `min..max`, thus `range(min..max)` will</span>
    <span class="doccomment">/// yield elements from min (inclusive) to max (exclusive).</span>
    <span class="doccomment">/// The range may also be entered as `(Bound&lt;T&gt;, Bound&lt;T&gt;)`, so for example</span>
    <span class="doccomment">/// `range((Excluded(4), Included(10)))` will yield a left-exclusive, right-inclusive</span>
    <span class="doccomment">/// range from 4 to 10.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Panics</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Panics if range `start &gt; end`.</span>
    <span class="doccomment">/// Panics if range `start == end` and both bounds are `Excluded`.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, i32&gt; = [&quot;Alice&quot;, &quot;Bob&quot;, &quot;Carol&quot;, &quot;Cheryl&quot;].iter()</span>
    <span class="doccomment">///                                                                       .map(|&amp;s| (s, 0))</span>
    <span class="doccomment">///                                                                       .collect();</span>
    <span class="doccomment">/// for (_, balance) in map.range_mut(&quot;B&quot;..&quot;Cheryl&quot;) {</span>
    <span class="doccomment">///     *balance += 100;</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// for (name, balance) in &amp;map {</span>
    <span class="doccomment">///     println!(&quot;{} =&gt; {}&quot;, name, balance);</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_range&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">range_mut</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span>, <span class="ident">R</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">range</span>: <span class="ident">R</span>) <span class="op">-&gt;</span> <span class="ident">RangeMut</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>
        <span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Ord</span>, <span class="ident">K</span>: <span class="ident">Borrow</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>, <span class="ident">R</span>: <span class="ident">RangeBounds</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>
    {
        <span class="kw">let</span> <span class="ident">root1</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>();
        <span class="kw">let</span> <span class="ident">root2</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="ident">root1</span>) };
        <span class="kw">let</span> (<span class="ident">f</span>, <span class="ident">b</span>) <span class="op">=</span> <span class="ident">range_search</span>(<span class="ident">root1</span>, <span class="ident">root2</span>, <span class="ident">range</span>);

        <span class="ident">RangeMut</span> {
            <span class="ident">front</span>: <span class="ident">f</span>,
            <span class="ident">back</span>: <span class="ident">b</span>,
            <span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
        }
    }

    <span class="doccomment">/// Gets the given key&#39;s corresponding entry in the map for in-place manipulation.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut count: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// // count the number of occurrences of letters in the vec</span>
    <span class="doccomment">/// for x in vec![&quot;a&quot;,&quot;b&quot;,&quot;a&quot;,&quot;c&quot;,&quot;a&quot;,&quot;b&quot;] {</span>
    <span class="doccomment">///     *count.entry(x).or_insert(0) += 1;</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(count[&quot;a&quot;], 3);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">entry</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">key</span>: <span class="ident">K</span>) <span class="op">-&gt;</span> <span class="ident">Entry</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="comment">// FIXME(@porglezomp) Avoid allocating if we don&#39;t insert</span>
        <span class="self">self</span>.<span class="ident">ensure_root_is_owned</span>();
        <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_tree</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>(), <span class="kw-2">&amp;</span><span class="ident">key</span>) {
            <span class="ident">Found</span>(<span class="ident">handle</span>) <span class="op">=&gt;</span> {
                <span class="ident">Occupied</span>(<span class="ident">OccupiedEntry</span> {
                    <span class="ident">handle</span>,
                    <span class="ident">length</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">length</span>,
                    <span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
                })
            }
            <span class="ident">GoDown</span>(<span class="ident">handle</span>) <span class="op">=&gt;</span> {
                <span class="ident">Vacant</span>(<span class="ident">VacantEntry</span> {
                    <span class="ident">key</span>,
                    <span class="ident">handle</span>,
                    <span class="ident">length</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">length</span>,
                    <span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
                })
            }
        }
    }

    <span class="kw">fn</span> <span class="ident">from_sorted_iter</span><span class="op">&lt;</span><span class="ident">I</span>: <span class="ident">Iterator</span><span class="op">&lt;</span><span class="ident">Item</span> <span class="op">=</span> (<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;&gt;</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">iter</span>: <span class="ident">I</span>) {
        <span class="self">self</span>.<span class="ident">ensure_root_is_owned</span>();
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_node</span> <span class="op">=</span> <span class="ident">last_leaf_edge</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>()).<span class="ident">into_node</span>();
        <span class="comment">// Iterate through all key-value pairs, pushing them into nodes at the right level.</span>
        <span class="kw">for</span> (<span class="ident">key</span>, <span class="ident">value</span>) <span class="kw">in</span> <span class="ident">iter</span> {
            <span class="comment">// Try to push key-value pair into the current leaf node.</span>
            <span class="kw">if</span> <span class="ident">cur_node</span>.<span class="ident">len</span>() <span class="op">&lt;</span> <span class="ident">node</span>::<span class="ident">CAPACITY</span> {
                <span class="ident">cur_node</span>.<span class="ident">push</span>(<span class="ident">key</span>, <span class="ident">value</span>);
            } <span class="kw">else</span> {
                <span class="comment">// No space left, go up and push there.</span>
                <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">open_node</span>;
                <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">test_node</span> <span class="op">=</span> <span class="ident">cur_node</span>.<span class="ident">forget_type</span>();
                <span class="kw">loop</span> {
                    <span class="kw">match</span> <span class="ident">test_node</span>.<span class="ident">ascend</span>() {
                        <span class="prelude-val">Ok</span>(<span class="ident">parent</span>) <span class="op">=&gt;</span> {
                            <span class="kw">let</span> <span class="ident">parent</span> <span class="op">=</span> <span class="ident">parent</span>.<span class="ident">into_node</span>();
                            <span class="kw">if</span> <span class="ident">parent</span>.<span class="ident">len</span>() <span class="op">&lt;</span> <span class="ident">node</span>::<span class="ident">CAPACITY</span> {
                                <span class="comment">// Found a node with space left, push here.</span>
                                <span class="ident">open_node</span> <span class="op">=</span> <span class="ident">parent</span>;
                                <span class="kw">break</span>;
                            } <span class="kw">else</span> {
                                <span class="comment">// Go up again.</span>
                                <span class="ident">test_node</span> <span class="op">=</span> <span class="ident">parent</span>.<span class="ident">forget_type</span>();
                            }
                        }
                        <span class="prelude-val">Err</span>(<span class="ident">node</span>) <span class="op">=&gt;</span> {
                            <span class="comment">// We are at the top, create a new root node and push there.</span>
                            <span class="ident">open_node</span> <span class="op">=</span> <span class="ident">node</span>.<span class="ident">into_root_mut</span>().<span class="ident">push_level</span>();
                            <span class="kw">break</span>;
                        }
                    }
                }

                <span class="comment">// Push key-value pair and new right subtree.</span>
                <span class="kw">let</span> <span class="ident">tree_height</span> <span class="op">=</span> <span class="ident">open_node</span>.<span class="ident">height</span>() <span class="op">-</span> <span class="number">1</span>;
                <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">right_tree</span> <span class="op">=</span> <span class="ident">node</span>::<span class="ident">Root</span>::<span class="ident">new_leaf</span>();
                <span class="kw">for</span> <span class="kw">_</span> <span class="kw">in</span> <span class="number">0</span>..<span class="ident">tree_height</span> {
                    <span class="ident">right_tree</span>.<span class="ident">push_level</span>();
                }
                <span class="ident">open_node</span>.<span class="ident">push</span>(<span class="ident">key</span>, <span class="ident">value</span>, <span class="ident">right_tree</span>);

                <span class="comment">// Go down to the right-most leaf again.</span>
                <span class="ident">cur_node</span> <span class="op">=</span> <span class="ident">last_leaf_edge</span>(<span class="ident">open_node</span>.<span class="ident">forget_type</span>()).<span class="ident">into_node</span>();
            }

            <span class="self">self</span>.<span class="ident">length</span> <span class="op">+=</span> <span class="number">1</span>;
        }
    }

    <span class="kw">fn</span> <span class="ident">fix_right_edge</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) {
        <span class="comment">// Handle underfull nodes, start from the top.</span>
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_node</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>();
        <span class="kw">while</span> <span class="kw">let</span> <span class="ident">Internal</span>(<span class="ident">internal</span>) <span class="op">=</span> <span class="ident">cur_node</span>.<span class="ident">force</span>() {
            <span class="comment">// Check if right-most child is underfull.</span>
            <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">last_edge</span> <span class="op">=</span> <span class="ident">internal</span>.<span class="ident">last_edge</span>();
            <span class="kw">let</span> <span class="ident">right_child_len</span> <span class="op">=</span> <span class="ident">last_edge</span>.<span class="ident">reborrow</span>().<span class="ident">descend</span>().<span class="ident">len</span>();
            <span class="kw">if</span> <span class="ident">right_child_len</span> <span class="op">&lt;</span> <span class="ident">node</span>::<span class="ident">MIN_LEN</span> {
                <span class="comment">// We need to steal.</span>
                <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">last_kv</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">last_edge</span>.<span class="ident">left_kv</span>() {
                    <span class="prelude-val">Ok</span>(<span class="ident">left</span>) <span class="op">=&gt;</span> <span class="ident">left</span>,
                    <span class="prelude-val">Err</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> <span class="macro">unreachable</span><span class="macro">!</span>(),
                };
                <span class="ident">last_kv</span>.<span class="ident">bulk_steal_left</span>(<span class="ident">node</span>::<span class="ident">MIN_LEN</span> <span class="op">-</span> <span class="ident">right_child_len</span>);
                <span class="ident">last_edge</span> <span class="op">=</span> <span class="ident">last_kv</span>.<span class="ident">right_edge</span>();
            }

            <span class="comment">// Go further down.</span>
            <span class="ident">cur_node</span> <span class="op">=</span> <span class="ident">last_edge</span>.<span class="ident">descend</span>();
        }
    }

    <span class="doccomment">/// Splits the collection into two at the given key. Returns everything after the given key,</span>
    <span class="doccomment">/// including the key.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut a = BTreeMap::new();</span>
    <span class="doccomment">/// a.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">/// a.insert(2, &quot;b&quot;);</span>
    <span class="doccomment">/// a.insert(3, &quot;c&quot;);</span>
    <span class="doccomment">/// a.insert(17, &quot;d&quot;);</span>
    <span class="doccomment">/// a.insert(41, &quot;e&quot;);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let b = a.split_off(&amp;3);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(a.len(), 2);</span>
    <span class="doccomment">/// assert_eq!(b.len(), 3);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(a[&amp;1], &quot;a&quot;);</span>
    <span class="doccomment">/// assert_eq!(a[&amp;2], &quot;b&quot;);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(b[&amp;3], &quot;c&quot;);</span>
    <span class="doccomment">/// assert_eq!(b[&amp;17], &quot;d&quot;);</span>
    <span class="doccomment">/// assert_eq!(b[&amp;41], &quot;e&quot;);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_split_off&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.11.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">split_off</span><span class="op">&lt;</span><span class="ident">Q</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">Ord</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">key</span>: <span class="kw-2">&amp;</span><span class="ident">Q</span>) <span class="op">-&gt;</span> <span class="self">Self</span>
        <span class="kw">where</span> <span class="ident">K</span>: <span class="ident">Borrow</span><span class="op">&lt;</span><span class="ident">Q</span><span class="op">&gt;</span>
    {
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">is_empty</span>() {
            <span class="kw">return</span> <span class="self">Self</span>::<span class="ident">new</span>();
        }

        <span class="kw">let</span> <span class="ident">total_num</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">len</span>();

        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">right</span> <span class="op">=</span> <span class="self">Self</span>::<span class="ident">new</span>();
        <span class="ident">right</span>.<span class="ident">root</span> <span class="op">=</span> <span class="ident">node</span>::<span class="ident">Root</span>::<span class="ident">new_leaf</span>();
        <span class="kw">for</span> <span class="kw">_</span> <span class="kw">in</span> <span class="number">0</span>..(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>().<span class="ident">height</span>()) {
            <span class="ident">right</span>.<span class="ident">root</span>.<span class="ident">push_level</span>();
        }

        {
            <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">left_node</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>();
            <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">right_node</span> <span class="op">=</span> <span class="ident">right</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>();

            <span class="kw">loop</span> {
                <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">split_edge</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_node</span>(<span class="ident">left_node</span>, <span class="ident">key</span>) {
                    <span class="comment">// key is going to the right tree</span>
                    <span class="ident">Found</span>(<span class="ident">handle</span>) <span class="op">=&gt;</span> <span class="ident">handle</span>.<span class="ident">left_edge</span>(),
                    <span class="ident">GoDown</span>(<span class="ident">handle</span>) <span class="op">=&gt;</span> <span class="ident">handle</span>,
                };

                <span class="ident">split_edge</span>.<span class="ident">move_suffix</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">right_node</span>);

                <span class="kw">match</span> (<span class="ident">split_edge</span>.<span class="ident">force</span>(), <span class="ident">right_node</span>.<span class="ident">force</span>()) {
                    (<span class="ident">Internal</span>(<span class="ident">edge</span>), <span class="ident">Internal</span>(<span class="ident">node</span>)) <span class="op">=&gt;</span> {
                        <span class="ident">left_node</span> <span class="op">=</span> <span class="ident">edge</span>.<span class="ident">descend</span>();
                        <span class="ident">right_node</span> <span class="op">=</span> <span class="ident">node</span>.<span class="ident">first_edge</span>().<span class="ident">descend</span>();
                    }
                    (<span class="ident">Leaf</span>(<span class="kw">_</span>), <span class="ident">Leaf</span>(<span class="kw">_</span>)) <span class="op">=&gt;</span> {
                        <span class="kw">break</span>;
                    }
                    <span class="kw">_</span> <span class="op">=&gt;</span> {
                        <span class="macro">unreachable</span><span class="macro">!</span>();
                    }
                }
            }
        }

        <span class="self">self</span>.<span class="ident">fix_right_border</span>();
        <span class="ident">right</span>.<span class="ident">fix_left_border</span>();

        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>().<span class="ident">height</span>() <span class="op">&lt;</span> <span class="ident">right</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>().<span class="ident">height</span>() {
            <span class="self">self</span>.<span class="ident">recalc_length</span>();
            <span class="ident">right</span>.<span class="ident">length</span> <span class="op">=</span> <span class="ident">total_num</span> <span class="op">-</span> <span class="self">self</span>.<span class="ident">len</span>();
        } <span class="kw">else</span> {
            <span class="ident">right</span>.<span class="ident">recalc_length</span>();
            <span class="self">self</span>.<span class="ident">length</span> <span class="op">=</span> <span class="ident">total_num</span> <span class="op">-</span> <span class="ident">right</span>.<span class="ident">len</span>();
        }

        <span class="ident">right</span>
    }

    <span class="doccomment">/// Calculates the number of elements if it is incorrect.</span>
    <span class="kw">fn</span> <span class="ident">recalc_length</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) {
        <span class="kw">fn</span> <span class="ident">dfs</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>(<span class="ident">node</span>: <span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Immut</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">LeafOrInternal</span><span class="op">&gt;</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
            <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">res</span> <span class="op">=</span> <span class="ident">node</span>.<span class="ident">len</span>();

            <span class="kw">if</span> <span class="kw">let</span> <span class="ident">Internal</span>(<span class="ident">node</span>) <span class="op">=</span> <span class="ident">node</span>.<span class="ident">force</span>() {
                <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">edge</span> <span class="op">=</span> <span class="ident">node</span>.<span class="ident">first_edge</span>();
                <span class="kw">loop</span> {
                    <span class="ident">res</span> <span class="op">+=</span> <span class="ident">dfs</span>(<span class="ident">edge</span>.<span class="ident">reborrow</span>().<span class="ident">descend</span>());
                    <span class="kw">match</span> <span class="ident">edge</span>.<span class="ident">right_kv</span>() {
                        <span class="prelude-val">Ok</span>(<span class="ident">right_kv</span>) <span class="op">=&gt;</span> {
                            <span class="ident">edge</span> <span class="op">=</span> <span class="ident">right_kv</span>.<span class="ident">right_edge</span>();
                        }
                        <span class="prelude-val">Err</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> {
                            <span class="kw">break</span>;
                        }
                    }
                }
            }

            <span class="ident">res</span>
        }

        <span class="self">self</span>.<span class="ident">length</span> <span class="op">=</span> <span class="ident">dfs</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>());
    }

    <span class="doccomment">/// Removes empty levels on the top.</span>
    <span class="kw">fn</span> <span class="ident">fix_top</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) {
        <span class="kw">loop</span> {
            {
                <span class="kw">let</span> <span class="ident">node</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>();
                <span class="kw">if</span> <span class="ident">node</span>.<span class="ident">height</span>() <span class="op">==</span> <span class="number">0</span> <span class="op">||</span> <span class="ident">node</span>.<span class="ident">len</span>() <span class="op">&gt;</span> <span class="number">0</span> {
                    <span class="kw">break</span>;
                }
            }
            <span class="self">self</span>.<span class="ident">root</span>.<span class="ident">pop_level</span>();
        }
    }

    <span class="kw">fn</span> <span class="ident">fix_right_border</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) {
        <span class="self">self</span>.<span class="ident">fix_top</span>();

        {
            <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_node</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>();

            <span class="kw">while</span> <span class="kw">let</span> <span class="ident">Internal</span>(<span class="ident">node</span>) <span class="op">=</span> <span class="ident">cur_node</span>.<span class="ident">force</span>() {
                <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">last_kv</span> <span class="op">=</span> <span class="ident">node</span>.<span class="ident">last_kv</span>();

                <span class="kw">if</span> <span class="ident">last_kv</span>.<span class="ident">can_merge</span>() {
                    <span class="ident">cur_node</span> <span class="op">=</span> <span class="ident">last_kv</span>.<span class="ident">merge</span>().<span class="ident">descend</span>();
                } <span class="kw">else</span> {
                    <span class="kw">let</span> <span class="ident">right_len</span> <span class="op">=</span> <span class="ident">last_kv</span>.<span class="ident">reborrow</span>().<span class="ident">right_edge</span>().<span class="ident">descend</span>().<span class="ident">len</span>();
                    <span class="comment">// `MINLEN + 1` to avoid readjust if merge happens on the next level.</span>
                    <span class="kw">if</span> <span class="ident">right_len</span> <span class="op">&lt;</span> <span class="ident">node</span>::<span class="ident">MIN_LEN</span> <span class="op">+</span> <span class="number">1</span> {
                        <span class="ident">last_kv</span>.<span class="ident">bulk_steal_left</span>(<span class="ident">node</span>::<span class="ident">MIN_LEN</span> <span class="op">+</span> <span class="number">1</span> <span class="op">-</span> <span class="ident">right_len</span>);
                    }
                    <span class="ident">cur_node</span> <span class="op">=</span> <span class="ident">last_kv</span>.<span class="ident">right_edge</span>().<span class="ident">descend</span>();
                }
            }
        }

        <span class="self">self</span>.<span class="ident">fix_top</span>();
    }

    <span class="doccomment">/// The symmetric clone of `fix_right_border`.</span>
    <span class="kw">fn</span> <span class="ident">fix_left_border</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) {
        <span class="self">self</span>.<span class="ident">fix_top</span>();

        {
            <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_node</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>();

            <span class="kw">while</span> <span class="kw">let</span> <span class="ident">Internal</span>(<span class="ident">node</span>) <span class="op">=</span> <span class="ident">cur_node</span>.<span class="ident">force</span>() {
                <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">first_kv</span> <span class="op">=</span> <span class="ident">node</span>.<span class="ident">first_kv</span>();

                <span class="kw">if</span> <span class="ident">first_kv</span>.<span class="ident">can_merge</span>() {
                    <span class="ident">cur_node</span> <span class="op">=</span> <span class="ident">first_kv</span>.<span class="ident">merge</span>().<span class="ident">descend</span>();
                } <span class="kw">else</span> {
                    <span class="kw">let</span> <span class="ident">left_len</span> <span class="op">=</span> <span class="ident">first_kv</span>.<span class="ident">reborrow</span>().<span class="ident">left_edge</span>().<span class="ident">descend</span>().<span class="ident">len</span>();
                    <span class="kw">if</span> <span class="ident">left_len</span> <span class="op">&lt;</span> <span class="ident">node</span>::<span class="ident">MIN_LEN</span> <span class="op">+</span> <span class="number">1</span> {
                        <span class="ident">first_kv</span>.<span class="ident">bulk_steal_right</span>(<span class="ident">node</span>::<span class="ident">MIN_LEN</span> <span class="op">+</span> <span class="number">1</span> <span class="op">-</span> <span class="ident">left_len</span>);
                    }
                    <span class="ident">cur_node</span> <span class="op">=</span> <span class="ident">first_kv</span>.<span class="ident">left_edge</span>().<span class="ident">descend</span>();
                }
            }
        }

        <span class="self">self</span>.<span class="ident">fix_top</span>();
    }

    <span class="doccomment">/// If the root node is the shared root node, allocate our own node.</span>
    <span class="kw">fn</span> <span class="ident">ensure_root_is_owned</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) {
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">root</span>.<span class="ident">is_shared_root</span>() {
            <span class="self">self</span>.<span class="ident">root</span> <span class="op">=</span> <span class="ident">node</span>::<span class="ident">Root</span>::<span class="ident">new_leaf</span>();
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">IntoIterator</span> <span class="kw">for</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> (<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span>);
    <span class="kw">type</span> <span class="ident">IntoIter</span> <span class="op">=</span> <span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>;

    <span class="kw">fn</span> <span class="ident">into_iter</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="self">self</span>.<span class="ident">iter</span>()
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> (<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span>);

    <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span>)<span class="op">&gt;</span> {
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">length</span> <span class="op">==</span> <span class="number">0</span> {
            <span class="prelude-val">None</span>
        } <span class="kw">else</span> {
            <span class="self">self</span>.<span class="ident">length</span> <span class="op">-=</span> <span class="number">1</span>;
            <span class="kw">unsafe</span> { <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">range</span>.<span class="ident">next_unchecked</span>()) }
        }
    }

    <span class="kw">fn</span> <span class="ident">size_hint</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> (<span class="ident">usize</span>, <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">usize</span><span class="op">&gt;</span>) {
        (<span class="self">self</span>.<span class="ident">length</span>, <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">length</span>))
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;fused&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.26.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">FusedIterator</span> <span class="kw">for</span> <span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">DoubleEndedIterator</span> <span class="kw">for</span> <span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">next_back</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span>)<span class="op">&gt;</span> {
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">length</span> <span class="op">==</span> <span class="number">0</span> {
            <span class="prelude-val">None</span>
        } <span class="kw">else</span> {
            <span class="self">self</span>.<span class="ident">length</span> <span class="op">-=</span> <span class="number">1</span>;
            <span class="kw">unsafe</span> { <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">range</span>.<span class="ident">next_back_unchecked</span>()) }
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">ExactSizeIterator</span> <span class="kw">for</span> <span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">len</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
        <span class="self">self</span>.<span class="ident">length</span>
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Iter</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="ident">Iter</span> {
            <span class="ident">range</span>: <span class="self">self</span>.<span class="ident">range</span>.<span class="ident">clone</span>(),
            <span class="ident">length</span>: <span class="self">self</span>.<span class="ident">length</span>,
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">IntoIterator</span> <span class="kw">for</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> (<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span>);
    <span class="kw">type</span> <span class="ident">IntoIter</span> <span class="op">=</span> <span class="ident">IterMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>;

    <span class="kw">fn</span> <span class="ident">into_iter</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">IterMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="self">self</span>.<span class="ident">iter_mut</span>()
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">IterMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> (<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span>);

    <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span>)<span class="op">&gt;</span> {
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">length</span> <span class="op">==</span> <span class="number">0</span> {
            <span class="prelude-val">None</span>
        } <span class="kw">else</span> {
            <span class="self">self</span>.<span class="ident">length</span> <span class="op">-=</span> <span class="number">1</span>;
            <span class="kw">unsafe</span> { <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">range</span>.<span class="ident">next_unchecked</span>()) }
        }
    }

    <span class="kw">fn</span> <span class="ident">size_hint</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> (<span class="ident">usize</span>, <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">usize</span><span class="op">&gt;</span>) {
        (<span class="self">self</span>.<span class="ident">length</span>, <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">length</span>))
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">DoubleEndedIterator</span> <span class="kw">for</span> <span class="ident">IterMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">next_back</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span>)<span class="op">&gt;</span> {
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">length</span> <span class="op">==</span> <span class="number">0</span> {
            <span class="prelude-val">None</span>
        } <span class="kw">else</span> {
            <span class="self">self</span>.<span class="ident">length</span> <span class="op">-=</span> <span class="number">1</span>;
            <span class="kw">unsafe</span> { <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">range</span>.<span class="ident">next_back_unchecked</span>()) }
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="lifetime">&#39;a</span>, <span class="ident">V</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">ExactSizeIterator</span> <span class="kw">for</span> <span class="ident">IterMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">len</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
        <span class="self">self</span>.<span class="ident">length</span>
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;fused&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.26.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">FusedIterator</span> <span class="kw">for</span> <span class="ident">IterMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">IntoIterator</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> (<span class="ident">K</span>, <span class="ident">V</span>);
    <span class="kw">type</span> <span class="ident">IntoIter</span> <span class="op">=</span> <span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>;

    <span class="kw">fn</span> <span class="ident">into_iter</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="kw">let</span> <span class="ident">root1</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">root</span>).<span class="ident">into_ref</span>() };
        <span class="kw">let</span> <span class="ident">root2</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">root</span>).<span class="ident">into_ref</span>() };
        <span class="kw">let</span> <span class="ident">len</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">length</span>;
        <span class="ident">mem</span>::<span class="ident">forget</span>(<span class="self">self</span>);

        <span class="ident">IntoIter</span> {
            <span class="ident">front</span>: <span class="ident">first_leaf_edge</span>(<span class="ident">root1</span>),
            <span class="ident">back</span>: <span class="ident">last_leaf_edge</span>(<span class="ident">root2</span>),
            <span class="ident">length</span>: <span class="ident">len</span>,
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_drop&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.7.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) {
        <span class="self">self</span>.<span class="ident">for_each</span>(<span class="ident">drop</span>);
        <span class="kw">unsafe</span> {
            <span class="kw">let</span> <span class="ident">leaf_node</span> <span class="op">=</span> <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">front</span>).<span class="ident">into_node</span>();
            <span class="kw">if</span> <span class="ident">leaf_node</span>.<span class="ident">is_shared_root</span>() {
                <span class="kw">return</span>;
            }

            <span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">first_parent</span>) <span class="op">=</span> <span class="ident">leaf_node</span>.<span class="ident">deallocate_and_ascend</span>() {
                <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_node</span> <span class="op">=</span> <span class="ident">first_parent</span>.<span class="ident">into_node</span>();
                <span class="kw">while</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">parent</span>) <span class="op">=</span> <span class="ident">cur_node</span>.<span class="ident">deallocate_and_ascend</span>() {
                    <span class="ident">cur_node</span> <span class="op">=</span> <span class="ident">parent</span>.<span class="ident">into_node</span>()
                }
            }
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> (<span class="ident">K</span>, <span class="ident">V</span>);

    <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;</span> {
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">length</span> <span class="op">==</span> <span class="number">0</span> {
            <span class="kw">return</span> <span class="prelude-val">None</span>;
        } <span class="kw">else</span> {
            <span class="self">self</span>.<span class="ident">length</span> <span class="op">-=</span> <span class="number">1</span>;
        }

        <span class="kw">let</span> <span class="ident">handle</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">front</span>) };

        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_handle</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">handle</span>.<span class="ident">right_kv</span>() {
            <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=&gt;</span> {
                <span class="kw">let</span> <span class="ident">k</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="ident">kv</span>.<span class="ident">reborrow</span>().<span class="ident">into_kv</span>().<span class="number">0</span>) };
                <span class="kw">let</span> <span class="ident">v</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="ident">kv</span>.<span class="ident">reborrow</span>().<span class="ident">into_kv</span>().<span class="number">1</span>) };
                <span class="self">self</span>.<span class="ident">front</span> <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">right_edge</span>();
                <span class="kw">return</span> <span class="prelude-val">Some</span>((<span class="ident">k</span>, <span class="ident">v</span>));
            }
            <span class="prelude-val">Err</span>(<span class="ident">last_edge</span>) <span class="op">=&gt;</span> <span class="kw">unsafe</span> {
                <span class="ident">unwrap_unchecked</span>(<span class="ident">last_edge</span>.<span class="ident">into_node</span>().<span class="ident">deallocate_and_ascend</span>())
            },
        };

        <span class="kw">loop</span> {
            <span class="kw">match</span> <span class="ident">cur_handle</span>.<span class="ident">right_kv</span>() {
                <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=&gt;</span> {
                    <span class="kw">let</span> <span class="ident">k</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="ident">kv</span>.<span class="ident">reborrow</span>().<span class="ident">into_kv</span>().<span class="number">0</span>) };
                    <span class="kw">let</span> <span class="ident">v</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="ident">kv</span>.<span class="ident">reborrow</span>().<span class="ident">into_kv</span>().<span class="number">1</span>) };
                    <span class="self">self</span>.<span class="ident">front</span> <span class="op">=</span> <span class="ident">first_leaf_edge</span>(<span class="ident">kv</span>.<span class="ident">right_edge</span>().<span class="ident">descend</span>());
                    <span class="kw">return</span> <span class="prelude-val">Some</span>((<span class="ident">k</span>, <span class="ident">v</span>));
                }
                <span class="prelude-val">Err</span>(<span class="ident">last_edge</span>) <span class="op">=&gt;</span> <span class="kw">unsafe</span> {
                    <span class="ident">cur_handle</span> <span class="op">=</span> <span class="ident">unwrap_unchecked</span>(<span class="ident">last_edge</span>.<span class="ident">into_node</span>().<span class="ident">deallocate_and_ascend</span>());
                },
            }
        }
    }

    <span class="kw">fn</span> <span class="ident">size_hint</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> (<span class="ident">usize</span>, <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">usize</span><span class="op">&gt;</span>) {
        (<span class="self">self</span>.<span class="ident">length</span>, <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">length</span>))
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">DoubleEndedIterator</span> <span class="kw">for</span> <span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">next_back</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;</span> {
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">length</span> <span class="op">==</span> <span class="number">0</span> {
            <span class="kw">return</span> <span class="prelude-val">None</span>;
        } <span class="kw">else</span> {
            <span class="self">self</span>.<span class="ident">length</span> <span class="op">-=</span> <span class="number">1</span>;
        }

        <span class="kw">let</span> <span class="ident">handle</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">back</span>) };

        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_handle</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">handle</span>.<span class="ident">left_kv</span>() {
            <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=&gt;</span> {
                <span class="kw">let</span> <span class="ident">k</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="ident">kv</span>.<span class="ident">reborrow</span>().<span class="ident">into_kv</span>().<span class="number">0</span>) };
                <span class="kw">let</span> <span class="ident">v</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="ident">kv</span>.<span class="ident">reborrow</span>().<span class="ident">into_kv</span>().<span class="number">1</span>) };
                <span class="self">self</span>.<span class="ident">back</span> <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">left_edge</span>();
                <span class="kw">return</span> <span class="prelude-val">Some</span>((<span class="ident">k</span>, <span class="ident">v</span>));
            }
            <span class="prelude-val">Err</span>(<span class="ident">last_edge</span>) <span class="op">=&gt;</span> <span class="kw">unsafe</span> {
                <span class="ident">unwrap_unchecked</span>(<span class="ident">last_edge</span>.<span class="ident">into_node</span>().<span class="ident">deallocate_and_ascend</span>())
            },
        };

        <span class="kw">loop</span> {
            <span class="kw">match</span> <span class="ident">cur_handle</span>.<span class="ident">left_kv</span>() {
                <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=&gt;</span> {
                    <span class="kw">let</span> <span class="ident">k</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="ident">kv</span>.<span class="ident">reborrow</span>().<span class="ident">into_kv</span>().<span class="number">0</span>) };
                    <span class="kw">let</span> <span class="ident">v</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="ident">kv</span>.<span class="ident">reborrow</span>().<span class="ident">into_kv</span>().<span class="number">1</span>) };
                    <span class="self">self</span>.<span class="ident">back</span> <span class="op">=</span> <span class="ident">last_leaf_edge</span>(<span class="ident">kv</span>.<span class="ident">left_edge</span>().<span class="ident">descend</span>());
                    <span class="kw">return</span> <span class="prelude-val">Some</span>((<span class="ident">k</span>, <span class="ident">v</span>));
                }
                <span class="prelude-val">Err</span>(<span class="ident">last_edge</span>) <span class="op">=&gt;</span> <span class="kw">unsafe</span> {
                    <span class="ident">cur_handle</span> <span class="op">=</span> <span class="ident">unwrap_unchecked</span>(<span class="ident">last_edge</span>.<span class="ident">into_node</span>().<span class="ident">deallocate_and_ascend</span>());
                },
            }
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">ExactSizeIterator</span> <span class="kw">for</span> <span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">len</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
        <span class="self">self</span>.<span class="ident">length</span>
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;fused&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.26.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">FusedIterator</span> <span class="kw">for</span> <span class="ident">IntoIter</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">Keys</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>;

    <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span><span class="op">&gt;</span> {
        <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">next</span>().<span class="ident">map</span>(<span class="op">|</span>(<span class="ident">k</span>, <span class="kw">_</span>)<span class="op">|</span> <span class="ident">k</span>)
    }

    <span class="kw">fn</span> <span class="ident">size_hint</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> (<span class="ident">usize</span>, <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">usize</span><span class="op">&gt;</span>) {
        <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">size_hint</span>()
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">DoubleEndedIterator</span> <span class="kw">for</span> <span class="ident">Keys</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">next_back</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span><span class="op">&gt;</span> {
        <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">next_back</span>().<span class="ident">map</span>(<span class="op">|</span>(<span class="ident">k</span>, <span class="kw">_</span>)<span class="op">|</span> <span class="ident">k</span>)
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">ExactSizeIterator</span> <span class="kw">for</span> <span class="ident">Keys</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">len</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
        <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">len</span>()
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;fused&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.26.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">FusedIterator</span> <span class="kw">for</span> <span class="ident">Keys</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">Keys</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Keys</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="ident">Keys</span> { <span class="ident">inner</span>: <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">clone</span>() }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">Values</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span>;

    <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">next</span>().<span class="ident">map</span>(<span class="op">|</span>(<span class="kw">_</span>, <span class="ident">v</span>)<span class="op">|</span> <span class="ident">v</span>)
    }

    <span class="kw">fn</span> <span class="ident">size_hint</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> (<span class="ident">usize</span>, <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">usize</span><span class="op">&gt;</span>) {
        <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">size_hint</span>()
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">DoubleEndedIterator</span> <span class="kw">for</span> <span class="ident">Values</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">next_back</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">next_back</span>().<span class="ident">map</span>(<span class="op">|</span>(<span class="kw">_</span>, <span class="ident">v</span>)<span class="op">|</span> <span class="ident">v</span>)
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">ExactSizeIterator</span> <span class="kw">for</span> <span class="ident">Values</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">len</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
        <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">len</span>()
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;fused&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.26.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">FusedIterator</span> <span class="kw">for</span> <span class="ident">Values</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">Values</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Values</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="ident">Values</span> { <span class="ident">inner</span>: <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">clone</span>() }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_range&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">Range</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> (<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span>);

    <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span>)<span class="op">&gt;</span> {
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">front</span> <span class="op">==</span> <span class="self">self</span>.<span class="ident">back</span> {
            <span class="prelude-val">None</span>
        } <span class="kw">else</span> {
            <span class="kw">unsafe</span> { <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">next_unchecked</span>()) }
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;map_values_mut&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.10.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">ValuesMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span>;

    <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">next</span>().<span class="ident">map</span>(<span class="op">|</span>(<span class="kw">_</span>, <span class="ident">v</span>)<span class="op">|</span> <span class="ident">v</span>)
    }

    <span class="kw">fn</span> <span class="ident">size_hint</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> (<span class="ident">usize</span>, <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">usize</span><span class="op">&gt;</span>) {
        <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">size_hint</span>()
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;map_values_mut&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.10.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">DoubleEndedIterator</span> <span class="kw">for</span> <span class="ident">ValuesMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">next_back</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">next_back</span>().<span class="ident">map</span>(<span class="op">|</span>(<span class="kw">_</span>, <span class="ident">v</span>)<span class="op">|</span> <span class="ident">v</span>)
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;map_values_mut&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.10.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">ExactSizeIterator</span> <span class="kw">for</span> <span class="ident">ValuesMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">len</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
        <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">len</span>()
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;fused&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.26.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">FusedIterator</span> <span class="kw">for</span> <span class="ident">ValuesMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {}


<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Range</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">next_unchecked</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> (<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span>) {
        <span class="kw">let</span> <span class="ident">handle</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">front</span>;

        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_handle</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">handle</span>.<span class="ident">right_kv</span>() {
            <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=&gt;</span> {
                <span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">into_kv</span>();
                <span class="self">self</span>.<span class="ident">front</span> <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">right_edge</span>();
                <span class="kw">return</span> <span class="ident">ret</span>;
            }
            <span class="prelude-val">Err</span>(<span class="ident">last_edge</span>) <span class="op">=&gt;</span> {
                <span class="kw">let</span> <span class="ident">next_level</span> <span class="op">=</span> <span class="ident">last_edge</span>.<span class="ident">into_node</span>().<span class="ident">ascend</span>().<span class="ident">ok</span>();
                <span class="ident">unwrap_unchecked</span>(<span class="ident">next_level</span>)
            }
        };

        <span class="kw">loop</span> {
            <span class="kw">match</span> <span class="ident">cur_handle</span>.<span class="ident">right_kv</span>() {
                <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=&gt;</span> {
                    <span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">into_kv</span>();
                    <span class="self">self</span>.<span class="ident">front</span> <span class="op">=</span> <span class="ident">first_leaf_edge</span>(<span class="ident">kv</span>.<span class="ident">right_edge</span>().<span class="ident">descend</span>());
                    <span class="kw">return</span> <span class="ident">ret</span>;
                }
                <span class="prelude-val">Err</span>(<span class="ident">last_edge</span>) <span class="op">=&gt;</span> {
                    <span class="kw">let</span> <span class="ident">next_level</span> <span class="op">=</span> <span class="ident">last_edge</span>.<span class="ident">into_node</span>().<span class="ident">ascend</span>().<span class="ident">ok</span>();
                    <span class="ident">cur_handle</span> <span class="op">=</span> <span class="ident">unwrap_unchecked</span>(<span class="ident">next_level</span>);
                }
            }
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_range&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">DoubleEndedIterator</span> <span class="kw">for</span> <span class="ident">Range</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">next_back</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span>)<span class="op">&gt;</span> {
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">front</span> <span class="op">==</span> <span class="self">self</span>.<span class="ident">back</span> {
            <span class="prelude-val">None</span>
        } <span class="kw">else</span> {
            <span class="kw">unsafe</span> { <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">next_back_unchecked</span>()) }
        }
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Range</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">next_back_unchecked</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> (<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span>) {
        <span class="kw">let</span> <span class="ident">handle</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">back</span>;

        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_handle</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">handle</span>.<span class="ident">left_kv</span>() {
            <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=&gt;</span> {
                <span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">into_kv</span>();
                <span class="self">self</span>.<span class="ident">back</span> <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">left_edge</span>();
                <span class="kw">return</span> <span class="ident">ret</span>;
            }
            <span class="prelude-val">Err</span>(<span class="ident">last_edge</span>) <span class="op">=&gt;</span> {
                <span class="kw">let</span> <span class="ident">next_level</span> <span class="op">=</span> <span class="ident">last_edge</span>.<span class="ident">into_node</span>().<span class="ident">ascend</span>().<span class="ident">ok</span>();
                <span class="ident">unwrap_unchecked</span>(<span class="ident">next_level</span>)
            }
        };

        <span class="kw">loop</span> {
            <span class="kw">match</span> <span class="ident">cur_handle</span>.<span class="ident">left_kv</span>() {
                <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=&gt;</span> {
                    <span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">into_kv</span>();
                    <span class="self">self</span>.<span class="ident">back</span> <span class="op">=</span> <span class="ident">last_leaf_edge</span>(<span class="ident">kv</span>.<span class="ident">left_edge</span>().<span class="ident">descend</span>());
                    <span class="kw">return</span> <span class="ident">ret</span>;
                }
                <span class="prelude-val">Err</span>(<span class="ident">last_edge</span>) <span class="op">=&gt;</span> {
                    <span class="kw">let</span> <span class="ident">next_level</span> <span class="op">=</span> <span class="ident">last_edge</span>.<span class="ident">into_node</span>().<span class="ident">ascend</span>().<span class="ident">ok</span>();
                    <span class="ident">cur_handle</span> <span class="op">=</span> <span class="ident">unwrap_unchecked</span>(<span class="ident">next_level</span>);
                }
            }
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;fused&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.26.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">FusedIterator</span> <span class="kw">for</span> <span class="ident">Range</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_range&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">Range</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Range</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="ident">Range</span> {
            <span class="ident">front</span>: <span class="self">self</span>.<span class="ident">front</span>,
            <span class="ident">back</span>: <span class="self">self</span>.<span class="ident">back</span>,
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_range&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">RangeMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> (<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span>);

    <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span>)<span class="op">&gt;</span> {
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">front</span> <span class="op">==</span> <span class="self">self</span>.<span class="ident">back</span> {
            <span class="prelude-val">None</span>
        } <span class="kw">else</span> {
            <span class="kw">unsafe</span> { <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">next_unchecked</span>()) }
        }
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">RangeMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">next_unchecked</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> (<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span>) {
        <span class="kw">let</span> <span class="ident">handle</span> <span class="op">=</span> <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">front</span>);

        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_handle</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">handle</span>.<span class="ident">right_kv</span>() {
            <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=&gt;</span> {
                <span class="kw">let</span> (<span class="ident">k</span>, <span class="ident">v</span>) <span class="op">=</span> <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="ident">kv</span>).<span class="ident">into_kv_mut</span>();
                <span class="self">self</span>.<span class="ident">front</span> <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">right_edge</span>();
                <span class="kw">return</span> (<span class="ident">k</span>, <span class="ident">v</span>);
            }
            <span class="prelude-val">Err</span>(<span class="ident">last_edge</span>) <span class="op">=&gt;</span> {
                <span class="kw">let</span> <span class="ident">next_level</span> <span class="op">=</span> <span class="ident">last_edge</span>.<span class="ident">into_node</span>().<span class="ident">ascend</span>().<span class="ident">ok</span>();
                <span class="ident">unwrap_unchecked</span>(<span class="ident">next_level</span>)
            }
        };

        <span class="kw">loop</span> {
            <span class="kw">match</span> <span class="ident">cur_handle</span>.<span class="ident">right_kv</span>() {
                <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=&gt;</span> {
                    <span class="kw">let</span> (<span class="ident">k</span>, <span class="ident">v</span>) <span class="op">=</span> <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="ident">kv</span>).<span class="ident">into_kv_mut</span>();
                    <span class="self">self</span>.<span class="ident">front</span> <span class="op">=</span> <span class="ident">first_leaf_edge</span>(<span class="ident">kv</span>.<span class="ident">right_edge</span>().<span class="ident">descend</span>());
                    <span class="kw">return</span> (<span class="ident">k</span>, <span class="ident">v</span>);
                }
                <span class="prelude-val">Err</span>(<span class="ident">last_edge</span>) <span class="op">=&gt;</span> {
                    <span class="kw">let</span> <span class="ident">next_level</span> <span class="op">=</span> <span class="ident">last_edge</span>.<span class="ident">into_node</span>().<span class="ident">ascend</span>().<span class="ident">ok</span>();
                    <span class="ident">cur_handle</span> <span class="op">=</span> <span class="ident">unwrap_unchecked</span>(<span class="ident">next_level</span>);
                }
            }
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;btree_range&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.17.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">DoubleEndedIterator</span> <span class="kw">for</span> <span class="ident">RangeMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">next_back</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span>)<span class="op">&gt;</span> {
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">front</span> <span class="op">==</span> <span class="self">self</span>.<span class="ident">back</span> {
            <span class="prelude-val">None</span>
        } <span class="kw">else</span> {
            <span class="kw">unsafe</span> { <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">next_back_unchecked</span>()) }
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;fused&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.26.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">FusedIterator</span> <span class="kw">for</span> <span class="ident">RangeMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {}

<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">RangeMut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">next_back_unchecked</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> (<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span>) {
        <span class="kw">let</span> <span class="ident">handle</span> <span class="op">=</span> <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">back</span>);

        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_handle</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">handle</span>.<span class="ident">left_kv</span>() {
            <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=&gt;</span> {
                <span class="kw">let</span> (<span class="ident">k</span>, <span class="ident">v</span>) <span class="op">=</span> <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="ident">kv</span>).<span class="ident">into_kv_mut</span>();
                <span class="self">self</span>.<span class="ident">back</span> <span class="op">=</span> <span class="ident">kv</span>.<span class="ident">left_edge</span>();
                <span class="kw">return</span> (<span class="ident">k</span>, <span class="ident">v</span>);
            }
            <span class="prelude-val">Err</span>(<span class="ident">last_edge</span>) <span class="op">=&gt;</span> {
                <span class="kw">let</span> <span class="ident">next_level</span> <span class="op">=</span> <span class="ident">last_edge</span>.<span class="ident">into_node</span>().<span class="ident">ascend</span>().<span class="ident">ok</span>();
                <span class="ident">unwrap_unchecked</span>(<span class="ident">next_level</span>)
            }
        };

        <span class="kw">loop</span> {
            <span class="kw">match</span> <span class="ident">cur_handle</span>.<span class="ident">left_kv</span>() {
                <span class="prelude-val">Ok</span>(<span class="ident">kv</span>) <span class="op">=&gt;</span> {
                    <span class="kw">let</span> (<span class="ident">k</span>, <span class="ident">v</span>) <span class="op">=</span> <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="ident">kv</span>).<span class="ident">into_kv_mut</span>();
                    <span class="self">self</span>.<span class="ident">back</span> <span class="op">=</span> <span class="ident">last_leaf_edge</span>(<span class="ident">kv</span>.<span class="ident">left_edge</span>().<span class="ident">descend</span>());
                    <span class="kw">return</span> (<span class="ident">k</span>, <span class="ident">v</span>);
                }
                <span class="prelude-val">Err</span>(<span class="ident">last_edge</span>) <span class="op">=&gt;</span> {
                    <span class="kw">let</span> <span class="ident">next_level</span> <span class="op">=</span> <span class="ident">last_edge</span>.<span class="ident">into_node</span>().<span class="ident">ascend</span>().<span class="ident">ok</span>();
                    <span class="ident">cur_handle</span> <span class="op">=</span> <span class="ident">unwrap_unchecked</span>(<span class="ident">next_level</span>);
                }
            }
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">Ord</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">FromIterator</span><span class="op">&lt;</span>(<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">from_iter</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="ident">IntoIterator</span><span class="op">&lt;</span><span class="ident">Item</span> <span class="op">=</span> (<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;&gt;</span>(<span class="ident">iter</span>: <span class="ident">T</span>) <span class="op">-&gt;</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span> <span class="op">=</span> <span class="ident">BTreeMap</span>::<span class="ident">new</span>();
        <span class="ident">map</span>.<span class="ident">extend</span>(<span class="ident">iter</span>);
        <span class="ident">map</span>
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">Ord</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Extend</span><span class="op">&lt;</span>(<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="attribute">#[<span class="ident">inline</span>]</span>
    <span class="kw">fn</span> <span class="ident">extend</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="ident">IntoIterator</span><span class="op">&lt;</span><span class="ident">Item</span> <span class="op">=</span> (<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;&gt;</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">iter</span>: <span class="ident">T</span>) {
        <span class="kw">for</span> (<span class="ident">k</span>, <span class="ident">v</span>) <span class="kw">in</span> <span class="ident">iter</span> {
            <span class="self">self</span>.<span class="ident">insert</span>(<span class="ident">k</span>, <span class="ident">v</span>);
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;extend_ref&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.2.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="ident">Ord</span> <span class="op">+</span> <span class="ident">Copy</span>, <span class="ident">V</span>: <span class="ident">Copy</span><span class="op">&gt;</span> <span class="ident">Extend</span><span class="op">&lt;</span>(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span>)<span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">extend</span><span class="op">&lt;</span><span class="ident">I</span>: <span class="ident">IntoIterator</span><span class="op">&lt;</span><span class="ident">Item</span> <span class="op">=</span> (<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">K</span>, <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">V</span>)<span class="op">&gt;&gt;</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">iter</span>: <span class="ident">I</span>) {
        <span class="self">self</span>.<span class="ident">extend</span>(<span class="ident">iter</span>.<span class="ident">into_iter</span>().<span class="ident">map</span>(<span class="op">|</span>(<span class="kw-2">&amp;</span><span class="ident">key</span>, <span class="kw-2">&amp;</span><span class="ident">value</span>)<span class="op">|</span> (<span class="ident">key</span>, <span class="ident">value</span>)));
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">Hash</span>, <span class="ident">V</span>: <span class="ident">Hash</span><span class="op">&gt;</span> <span class="ident">Hash</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">hash</span><span class="op">&lt;</span><span class="ident">H</span>: <span class="ident">Hasher</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">state</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">H</span>) {
        <span class="kw">for</span> <span class="ident">elt</span> <span class="kw">in</span> <span class="self">self</span> {
            <span class="ident">elt</span>.<span class="ident">hash</span>(<span class="ident">state</span>);
        }
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">Ord</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="doccomment">/// Creates an empty `BTreeMap&lt;K, V&gt;`.</span>
    <span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-&gt;</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="ident">BTreeMap</span>::<span class="ident">new</span>()
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">PartialEq</span>, <span class="ident">V</span>: <span class="ident">PartialEq</span><span class="op">&gt;</span> <span class="ident">PartialEq</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">eq</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&amp;</span><span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
        <span class="self">self</span>.<span class="ident">len</span>() <span class="op">==</span> <span class="ident">other</span>.<span class="ident">len</span>() <span class="op">&amp;&amp;</span> <span class="self">self</span>.<span class="ident">iter</span>().<span class="ident">zip</span>(<span class="ident">other</span>).<span class="ident">all</span>(<span class="op">|</span>(<span class="ident">a</span>, <span class="ident">b</span>)<span class="op">|</span> <span class="ident">a</span> <span class="op">==</span> <span class="ident">b</span>)
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">Eq</span>, <span class="ident">V</span>: <span class="ident">Eq</span><span class="op">&gt;</span> <span class="ident">Eq</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">PartialOrd</span>, <span class="ident">V</span>: <span class="ident">PartialOrd</span><span class="op">&gt;</span> <span class="ident">PartialOrd</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="attribute">#[<span class="ident">inline</span>]</span>
    <span class="kw">fn</span> <span class="ident">partial_cmp</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&amp;</span><span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">Ordering</span><span class="op">&gt;</span> {
        <span class="self">self</span>.<span class="ident">iter</span>().<span class="ident">partial_cmp</span>(<span class="ident">other</span>.<span class="ident">iter</span>())
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">Ord</span>, <span class="ident">V</span>: <span class="ident">Ord</span><span class="op">&gt;</span> <span class="ident">Ord</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="attribute">#[<span class="ident">inline</span>]</span>
    <span class="kw">fn</span> <span class="ident">cmp</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&amp;</span><span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>) <span class="op">-&gt;</span> <span class="ident">Ordering</span> {
        <span class="self">self</span>.<span class="ident">iter</span>().<span class="ident">cmp</span>(<span class="ident">other</span>.<span class="ident">iter</span>())
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">Debug</span>, <span class="ident">V</span>: <span class="ident">Debug</span><span class="op">&gt;</span> <span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="ident">f</span>.<span class="ident">debug_map</span>().<span class="ident">entries</span>(<span class="self">self</span>.<span class="ident">iter</span>()).<span class="ident">finish</span>()
    }
}

<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="ident">Ord</span>, <span class="ident">Q</span>: <span class="question-mark">?</span><span class="ident">Sized</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Index</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">Q</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>
    <span class="kw">where</span> <span class="ident">K</span>: <span class="ident">Borrow</span><span class="op">&lt;</span><span class="ident">Q</span><span class="op">&gt;</span>,
          <span class="ident">Q</span>: <span class="ident">Ord</span>
{
    <span class="kw">type</span> <span class="ident">Output</span> <span class="op">=</span> <span class="ident">V</span>;

    <span class="doccomment">/// Returns a reference to the value corresponding to the supplied key.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Panics</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Panics if the key is not present in the `BTreeMap`.</span>
    <span class="attribute">#[<span class="ident">inline</span>]</span>
    <span class="kw">fn</span> <span class="ident">index</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">key</span>: <span class="kw-2">&amp;</span><span class="ident">Q</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="ident">V</span> {
        <span class="self">self</span>.<span class="ident">get</span>(<span class="ident">key</span>).<span class="ident">expect</span>(<span class="string">&quot;no entry found for key&quot;</span>)
    }
}

<span class="kw">fn</span> <span class="ident">first_leaf_edge</span><span class="op">&lt;</span><span class="ident">BorrowType</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>
    (<span class="kw-2">mut</span> <span class="ident">node</span>: <span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">BorrowType</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">LeafOrInternal</span><span class="op">&gt;</span>)
     <span class="op">-&gt;</span> <span class="ident">Handle</span><span class="op">&lt;</span><span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">BorrowType</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Leaf</span><span class="op">&gt;</span>, <span class="ident">marker</span>::<span class="ident">Edge</span><span class="op">&gt;</span> {
    <span class="kw">loop</span> {
        <span class="kw">match</span> <span class="ident">node</span>.<span class="ident">force</span>() {
            <span class="ident">Leaf</span>(<span class="ident">leaf</span>) <span class="op">=&gt;</span> <span class="kw">return</span> <span class="ident">leaf</span>.<span class="ident">first_edge</span>(),
            <span class="ident">Internal</span>(<span class="ident">internal</span>) <span class="op">=&gt;</span> {
                <span class="ident">node</span> <span class="op">=</span> <span class="ident">internal</span>.<span class="ident">first_edge</span>().<span class="ident">descend</span>();
            }
        }
    }
}

<span class="kw">fn</span> <span class="ident">last_leaf_edge</span><span class="op">&lt;</span><span class="ident">BorrowType</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>
    (<span class="kw-2">mut</span> <span class="ident">node</span>: <span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">BorrowType</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">LeafOrInternal</span><span class="op">&gt;</span>)
     <span class="op">-&gt;</span> <span class="ident">Handle</span><span class="op">&lt;</span><span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">BorrowType</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Leaf</span><span class="op">&gt;</span>, <span class="ident">marker</span>::<span class="ident">Edge</span><span class="op">&gt;</span> {
    <span class="kw">loop</span> {
        <span class="kw">match</span> <span class="ident">node</span>.<span class="ident">force</span>() {
            <span class="ident">Leaf</span>(<span class="ident">leaf</span>) <span class="op">=&gt;</span> <span class="kw">return</span> <span class="ident">leaf</span>.<span class="ident">last_edge</span>(),
            <span class="ident">Internal</span>(<span class="ident">internal</span>) <span class="op">=&gt;</span> {
                <span class="ident">node</span> <span class="op">=</span> <span class="ident">internal</span>.<span class="ident">last_edge</span>().<span class="ident">descend</span>();
            }
        }
    }
}

<span class="kw">fn</span> <span class="ident">range_search</span><span class="op">&lt;</span><span class="ident">BorrowType</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">Q</span>: <span class="question-mark">?</span><span class="ident">Sized</span>, <span class="ident">R</span>: <span class="ident">RangeBounds</span><span class="op">&lt;</span><span class="ident">Q</span><span class="op">&gt;&gt;</span>(
    <span class="ident">root1</span>: <span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">BorrowType</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">LeafOrInternal</span><span class="op">&gt;</span>,
    <span class="ident">root2</span>: <span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">BorrowType</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">LeafOrInternal</span><span class="op">&gt;</span>,
    <span class="ident">range</span>: <span class="ident">R</span>
)<span class="op">-&gt;</span> (<span class="ident">Handle</span><span class="op">&lt;</span><span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">BorrowType</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Leaf</span><span class="op">&gt;</span>, <span class="ident">marker</span>::<span class="ident">Edge</span><span class="op">&gt;</span>,
     <span class="ident">Handle</span><span class="op">&lt;</span><span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">BorrowType</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Leaf</span><span class="op">&gt;</span>, <span class="ident">marker</span>::<span class="ident">Edge</span><span class="op">&gt;</span>)
        <span class="kw">where</span> <span class="ident">Q</span>: <span class="ident">Ord</span>, <span class="ident">K</span>: <span class="ident">Borrow</span><span class="op">&lt;</span><span class="ident">Q</span><span class="op">&gt;</span>
{
    <span class="kw">match</span> (<span class="ident">range</span>.<span class="ident">start_bound</span>(), <span class="ident">range</span>.<span class="ident">end_bound</span>()) {
        (<span class="ident">Excluded</span>(<span class="ident">s</span>), <span class="ident">Excluded</span>(<span class="ident">e</span>)) <span class="kw">if</span> <span class="ident">s</span><span class="op">==</span><span class="ident">e</span> <span class="op">=&gt;</span>
            <span class="macro">panic</span><span class="macro">!</span>(<span class="string">&quot;range start and end are equal and excluded in BTreeMap&quot;</span>),
        (<span class="ident">Included</span>(<span class="ident">s</span>), <span class="ident">Included</span>(<span class="ident">e</span>)) <span class="op">|</span>
        (<span class="ident">Included</span>(<span class="ident">s</span>), <span class="ident">Excluded</span>(<span class="ident">e</span>)) <span class="op">|</span>
        (<span class="ident">Excluded</span>(<span class="ident">s</span>), <span class="ident">Included</span>(<span class="ident">e</span>)) <span class="op">|</span>
        (<span class="ident">Excluded</span>(<span class="ident">s</span>), <span class="ident">Excluded</span>(<span class="ident">e</span>)) <span class="kw">if</span> <span class="ident">s</span><span class="op">&gt;</span><span class="ident">e</span> <span class="op">=&gt;</span>
            <span class="macro">panic</span><span class="macro">!</span>(<span class="string">&quot;range start is greater than range end in BTreeMap&quot;</span>),
        <span class="kw">_</span> <span class="op">=&gt;</span> {},
    };

    <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">min_node</span> <span class="op">=</span> <span class="ident">root1</span>;
    <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">max_node</span> <span class="op">=</span> <span class="ident">root2</span>;
    <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">min_found</span> <span class="op">=</span> <span class="bool-val">false</span>;
    <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">max_found</span> <span class="op">=</span> <span class="bool-val">false</span>;
    <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">diverged</span> <span class="op">=</span> <span class="bool-val">false</span>;

    <span class="kw">loop</span> {
        <span class="kw">let</span> <span class="ident">min_edge</span> <span class="op">=</span> <span class="kw">match</span> (<span class="ident">min_found</span>, <span class="ident">range</span>.<span class="ident">start_bound</span>()) {
            (<span class="bool-val">false</span>, <span class="ident">Included</span>(<span class="ident">key</span>)) <span class="op">=&gt;</span> <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_linear</span>(<span class="kw-2">&amp;</span><span class="ident">min_node</span>, <span class="ident">key</span>) {
                (<span class="ident">i</span>, <span class="bool-val">true</span>) <span class="op">=&gt;</span> { <span class="ident">min_found</span> <span class="op">=</span> <span class="bool-val">true</span>; <span class="ident">i</span> },
                (<span class="ident">i</span>, <span class="bool-val">false</span>) <span class="op">=&gt;</span> <span class="ident">i</span>,
            },
            (<span class="bool-val">false</span>, <span class="ident">Excluded</span>(<span class="ident">key</span>)) <span class="op">=&gt;</span> <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_linear</span>(<span class="kw-2">&amp;</span><span class="ident">min_node</span>, <span class="ident">key</span>) {
                (<span class="ident">i</span>, <span class="bool-val">true</span>) <span class="op">=&gt;</span> { <span class="ident">min_found</span> <span class="op">=</span> <span class="bool-val">true</span>; <span class="ident">i</span><span class="op">+</span><span class="number">1</span> },
                (<span class="ident">i</span>, <span class="bool-val">false</span>) <span class="op">=&gt;</span> <span class="ident">i</span>,
            },
            (<span class="kw">_</span>, <span class="ident">Unbounded</span>) <span class="op">=&gt;</span> <span class="number">0</span>,
            (<span class="bool-val">true</span>, <span class="ident">Included</span>(<span class="kw">_</span>)) <span class="op">=&gt;</span> <span class="ident">min_node</span>.<span class="ident">keys</span>().<span class="ident">len</span>(),
            (<span class="bool-val">true</span>, <span class="ident">Excluded</span>(<span class="kw">_</span>)) <span class="op">=&gt;</span> <span class="number">0</span>,
        };

        <span class="kw">let</span> <span class="ident">max_edge</span> <span class="op">=</span> <span class="kw">match</span> (<span class="ident">max_found</span>, <span class="ident">range</span>.<span class="ident">end_bound</span>()) {
            (<span class="bool-val">false</span>, <span class="ident">Included</span>(<span class="ident">key</span>)) <span class="op">=&gt;</span> <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_linear</span>(<span class="kw-2">&amp;</span><span class="ident">max_node</span>, <span class="ident">key</span>) {
                (<span class="ident">i</span>, <span class="bool-val">true</span>) <span class="op">=&gt;</span> { <span class="ident">max_found</span> <span class="op">=</span> <span class="bool-val">true</span>; <span class="ident">i</span><span class="op">+</span><span class="number">1</span> },
                (<span class="ident">i</span>, <span class="bool-val">false</span>) <span class="op">=&gt;</span> <span class="ident">i</span>,
            },
            (<span class="bool-val">false</span>, <span class="ident">Excluded</span>(<span class="ident">key</span>)) <span class="op">=&gt;</span> <span class="kw">match</span> <span class="ident">search</span>::<span class="ident">search_linear</span>(<span class="kw-2">&amp;</span><span class="ident">max_node</span>, <span class="ident">key</span>) {
                (<span class="ident">i</span>, <span class="bool-val">true</span>) <span class="op">=&gt;</span> { <span class="ident">max_found</span> <span class="op">=</span> <span class="bool-val">true</span>; <span class="ident">i</span> },
                (<span class="ident">i</span>, <span class="bool-val">false</span>) <span class="op">=&gt;</span> <span class="ident">i</span>,
            },
            (<span class="kw">_</span>, <span class="ident">Unbounded</span>) <span class="op">=&gt;</span> <span class="ident">max_node</span>.<span class="ident">keys</span>().<span class="ident">len</span>(),
            (<span class="bool-val">true</span>, <span class="ident">Included</span>(<span class="kw">_</span>)) <span class="op">=&gt;</span> <span class="number">0</span>,
            (<span class="bool-val">true</span>, <span class="ident">Excluded</span>(<span class="kw">_</span>)) <span class="op">=&gt;</span> <span class="ident">max_node</span>.<span class="ident">keys</span>().<span class="ident">len</span>(),
        };

        <span class="kw">if</span> <span class="op">!</span><span class="ident">diverged</span> {
            <span class="kw">if</span> <span class="ident">max_edge</span> <span class="op">&lt;</span> <span class="ident">min_edge</span> { <span class="macro">panic</span><span class="macro">!</span>(<span class="string">&quot;Ord is ill-defined in BTreeMap range&quot;</span>) }
            <span class="kw">if</span> <span class="ident">min_edge</span> <span class="op">!=</span> <span class="ident">max_edge</span> { <span class="ident">diverged</span> <span class="op">=</span> <span class="bool-val">true</span>; }
        }

        <span class="kw">let</span> <span class="ident">front</span> <span class="op">=</span> <span class="ident">Handle</span>::<span class="ident">new_edge</span>(<span class="ident">min_node</span>, <span class="ident">min_edge</span>);
        <span class="kw">let</span> <span class="ident">back</span> <span class="op">=</span> <span class="ident">Handle</span>::<span class="ident">new_edge</span>(<span class="ident">max_node</span>, <span class="ident">max_edge</span>);
        <span class="kw">match</span> (<span class="ident">front</span>.<span class="ident">force</span>(), <span class="ident">back</span>.<span class="ident">force</span>()) {
            (<span class="ident">Leaf</span>(<span class="ident">f</span>), <span class="ident">Leaf</span>(<span class="ident">b</span>)) <span class="op">=&gt;</span> {
                <span class="kw">return</span> (<span class="ident">f</span>, <span class="ident">b</span>);
            },
            (<span class="ident">Internal</span>(<span class="ident">min_int</span>), <span class="ident">Internal</span>(<span class="ident">max_int</span>)) <span class="op">=&gt;</span> {
                <span class="ident">min_node</span> <span class="op">=</span> <span class="ident">min_int</span>.<span class="ident">descend</span>();
                <span class="ident">max_node</span> <span class="op">=</span> <span class="ident">max_int</span>.<span class="ident">descend</span>();
            },
            <span class="kw">_</span> <span class="op">=&gt;</span> <span class="macro">unreachable</span><span class="macro">!</span>(<span class="string">&quot;BTreeMap has different depths&quot;</span>),
        };
    }
}

<span class="attribute">#[<span class="ident">inline</span>(<span class="ident">always</span>)]</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">unwrap_unchecked</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>(<span class="ident">val</span>: <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>) <span class="op">-&gt;</span> <span class="ident">T</span> {
    <span class="ident">val</span>.<span class="ident">unwrap_or_else</span>(<span class="op">||</span> {
        <span class="kw">if</span> <span class="macro">cfg</span><span class="macro">!</span>(<span class="ident">debug_assertions</span>) {
            <span class="macro">panic</span><span class="macro">!</span>(<span class="string">&quot;&#39;unchecked&#39; unwrap on None in BTreeMap&quot;</span>);
        } <span class="kw">else</span> {
            <span class="ident">intrinsics</span>::<span class="ident">unreachable</span>();
        }
    })
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">BTreeMap</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="doccomment">/// Gets an iterator over the entries of the map, sorted by key.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map = BTreeMap::new();</span>
    <span class="doccomment">/// map.insert(3, &quot;c&quot;);</span>
    <span class="doccomment">/// map.insert(2, &quot;b&quot;);</span>
    <span class="doccomment">/// map.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// for (key, value) in map.iter() {</span>
    <span class="doccomment">///     println!(&quot;{}: {}&quot;, key, value);</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let (first_key, first_value) = map.iter().next().unwrap();</span>
    <span class="doccomment">/// assert_eq!((*first_key, *first_value), (1, &quot;a&quot;));</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">iter</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Iter</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="ident">Iter</span> {
            <span class="ident">range</span>: <span class="ident">Range</span> {
                <span class="ident">front</span>: <span class="ident">first_leaf_edge</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>()),
                <span class="ident">back</span>: <span class="ident">last_leaf_edge</span>(<span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_ref</span>()),
            },
            <span class="ident">length</span>: <span class="self">self</span>.<span class="ident">length</span>,
        }
    }

    <span class="doccomment">/// Gets a mutable iterator over the entries of the map, sorted by key.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map = BTreeMap::new();</span>
    <span class="doccomment">/// map.insert(&quot;a&quot;, 1);</span>
    <span class="doccomment">/// map.insert(&quot;b&quot;, 2);</span>
    <span class="doccomment">/// map.insert(&quot;c&quot;, 3);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// // add 10 to the value if the key isn&#39;t &quot;a&quot;</span>
    <span class="doccomment">/// for (key, value) in map.iter_mut() {</span>
    <span class="doccomment">///     if key != &amp;&quot;a&quot; {</span>
    <span class="doccomment">///         *value += 10;</span>
    <span class="doccomment">///     }</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">iter_mut</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">IterMut</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="kw">let</span> <span class="ident">root1</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">root</span>.<span class="ident">as_mut</span>();
        <span class="kw">let</span> <span class="ident">root2</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="ident">root1</span>) };
        <span class="ident">IterMut</span> {
            <span class="ident">range</span>: <span class="ident">RangeMut</span> {
                <span class="ident">front</span>: <span class="ident">first_leaf_edge</span>(<span class="ident">root1</span>),
                <span class="ident">back</span>: <span class="ident">last_leaf_edge</span>(<span class="ident">root2</span>),
                <span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
            },
            <span class="ident">length</span>: <span class="self">self</span>.<span class="ident">length</span>,
        }
    }

    <span class="doccomment">/// Gets an iterator over the keys of the map, in sorted order.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut a = BTreeMap::new();</span>
    <span class="doccomment">/// a.insert(2, &quot;b&quot;);</span>
    <span class="doccomment">/// a.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let keys: Vec&lt;_&gt; = a.keys().cloned().collect();</span>
    <span class="doccomment">/// assert_eq!(keys, [1, 2]);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">keys</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Keys</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="ident">Keys</span> { <span class="ident">inner</span>: <span class="self">self</span>.<span class="ident">iter</span>() }
    }

    <span class="doccomment">/// Gets an iterator over the values of the map, in order by key.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut a = BTreeMap::new();</span>
    <span class="doccomment">/// a.insert(1, &quot;hello&quot;);</span>
    <span class="doccomment">/// a.insert(2, &quot;goodbye&quot;);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let values: Vec&lt;&amp;str&gt; = a.values().cloned().collect();</span>
    <span class="doccomment">/// assert_eq!(values, [&quot;hello&quot;, &quot;goodbye&quot;]);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">values</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Values</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="ident">Values</span> { <span class="ident">inner</span>: <span class="self">self</span>.<span class="ident">iter</span>() }
    }

    <span class="doccomment">/// Gets a mutable iterator over the values of the map, in order by key.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut a = BTreeMap::new();</span>
    <span class="doccomment">/// a.insert(1, String::from(&quot;hello&quot;));</span>
    <span class="doccomment">/// a.insert(2, String::from(&quot;goodbye&quot;));</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// for value in a.values_mut() {</span>
    <span class="doccomment">///     value.push_str(&quot;!&quot;);</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let values: Vec&lt;String&gt; = a.values().cloned().collect();</span>
    <span class="doccomment">/// assert_eq!(values, [String::from(&quot;hello!&quot;),</span>
    <span class="doccomment">///                     String::from(&quot;goodbye!&quot;)]);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;map_values_mut&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.10.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">values_mut</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">ValuesMut</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
        <span class="ident">ValuesMut</span> { <span class="ident">inner</span>: <span class="self">self</span>.<span class="ident">iter_mut</span>() }
    }

    <span class="doccomment">/// Returns the number of elements in the map.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut a = BTreeMap::new();</span>
    <span class="doccomment">/// assert_eq!(a.len(), 0);</span>
    <span class="doccomment">/// a.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">/// assert_eq!(a.len(), 1);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">len</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
        <span class="self">self</span>.<span class="ident">length</span>
    }

    <span class="doccomment">/// Returns `true` if the map contains no elements.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Basic usage:</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut a = BTreeMap::new();</span>
    <span class="doccomment">/// assert!(a.is_empty());</span>
    <span class="doccomment">/// a.insert(1, &quot;a&quot;);</span>
    <span class="doccomment">/// assert!(!a.is_empty());</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">is_empty</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
        <span class="self">self</span>.<span class="ident">len</span>() <span class="op">==</span> <span class="number">0</span>
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="ident">Ord</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">Entry</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="doccomment">/// Ensures a value is in the entry by inserting the default if empty, and returns</span>
    <span class="doccomment">/// a mutable reference to the value in the entry.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">/// map.entry(&quot;poneyland&quot;).or_insert(12);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(map[&quot;poneyland&quot;], 12);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">or_insert</span>(<span class="self">self</span>, <span class="ident">default</span>: <span class="ident">V</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span> {
        <span class="kw">match</span> <span class="self">self</span> {
            <span class="ident">Occupied</span>(<span class="ident">entry</span>) <span class="op">=&gt;</span> <span class="ident">entry</span>.<span class="ident">into_mut</span>(),
            <span class="ident">Vacant</span>(<span class="ident">entry</span>) <span class="op">=&gt;</span> <span class="ident">entry</span>.<span class="ident">insert</span>(<span class="ident">default</span>),
        }
    }

    <span class="doccomment">/// Ensures a value is in the entry by inserting the result of the default function if empty,</span>
    <span class="doccomment">/// and returns a mutable reference to the value in the entry.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, String&gt; = BTreeMap::new();</span>
    <span class="doccomment">/// let s = &quot;hoho&quot;.to_string();</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// map.entry(&quot;poneyland&quot;).or_insert_with(|| s);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(map[&quot;poneyland&quot;], &quot;hoho&quot;.to_string());</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">or_insert_with</span><span class="op">&lt;</span><span class="ident">F</span>: <span class="ident">FnOnce</span>() <span class="op">-&gt;</span> <span class="ident">V</span><span class="op">&gt;</span>(<span class="self">self</span>, <span class="ident">default</span>: <span class="ident">F</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span> {
        <span class="kw">match</span> <span class="self">self</span> {
            <span class="ident">Occupied</span>(<span class="ident">entry</span>) <span class="op">=&gt;</span> <span class="ident">entry</span>.<span class="ident">into_mut</span>(),
            <span class="ident">Vacant</span>(<span class="ident">entry</span>) <span class="op">=&gt;</span> <span class="ident">entry</span>.<span class="ident">insert</span>(<span class="ident">default</span>()),
        }
    }

    <span class="doccomment">/// Returns a reference to this entry&#39;s key.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">/// assert_eq!(map.entry(&quot;poneyland&quot;).key(), &amp;&quot;poneyland&quot;);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;map_entry_keys&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.10.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">key</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="ident">K</span> {
        <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {
            <span class="ident">Occupied</span>(<span class="kw-2">ref</span> <span class="ident">entry</span>) <span class="op">=&gt;</span> <span class="ident">entry</span>.<span class="ident">key</span>(),
            <span class="ident">Vacant</span>(<span class="kw-2">ref</span> <span class="ident">entry</span>) <span class="op">=&gt;</span> <span class="ident">entry</span>.<span class="ident">key</span>(),
        }
    }

    <span class="doccomment">/// Provides in-place mutable access to an occupied entry before any</span>
    <span class="doccomment">/// potential inserts into the map.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// map.entry(&quot;poneyland&quot;)</span>
    <span class="doccomment">///    .and_modify(|e| { *e += 1 })</span>
    <span class="doccomment">///    .or_insert(42);</span>
    <span class="doccomment">/// assert_eq!(map[&quot;poneyland&quot;], 42);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// map.entry(&quot;poneyland&quot;)</span>
    <span class="doccomment">///    .and_modify(|e| { *e += 1 })</span>
    <span class="doccomment">///    .or_insert(42);</span>
    <span class="doccomment">/// assert_eq!(map[&quot;poneyland&quot;], 43);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;entry_and_modify&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.26.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">and_modify</span><span class="op">&lt;</span><span class="ident">F</span><span class="op">&gt;</span>(<span class="self">self</span>, <span class="ident">f</span>: <span class="ident">F</span>) <span class="op">-&gt;</span> <span class="self">Self</span>
        <span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">V</span>)
    {
        <span class="kw">match</span> <span class="self">self</span> {
            <span class="ident">Occupied</span>(<span class="kw-2">mut</span> <span class="ident">entry</span>) <span class="op">=&gt;</span> {
                <span class="ident">f</span>(<span class="ident">entry</span>.<span class="ident">get_mut</span>());
                <span class="ident">Occupied</span>(<span class="ident">entry</span>)
            },
            <span class="ident">Vacant</span>(<span class="ident">entry</span>) <span class="op">=&gt;</span> <span class="ident">Vacant</span>(<span class="ident">entry</span>),
        }
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="ident">Ord</span>, <span class="ident">V</span>: <span class="ident">Default</span><span class="op">&gt;</span> <span class="ident">Entry</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;entry_or_default&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.28.0&quot;</span>)]</span>
    <span class="doccomment">/// Ensures a value is in the entry by inserting the default value if empty,</span>
    <span class="doccomment">/// and returns a mutable reference to the value in the entry.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// # fn main() {</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, Option&lt;usize&gt;&gt; = BTreeMap::new();</span>
    <span class="doccomment">/// map.entry(&quot;poneyland&quot;).or_default();</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(map[&quot;poneyland&quot;], None);</span>
    <span class="doccomment">/// # }</span>
    <span class="doccomment">/// ```</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">or_default</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span> {
        <span class="kw">match</span> <span class="self">self</span> {
            <span class="ident">Occupied</span>(<span class="ident">entry</span>) <span class="op">=&gt;</span> <span class="ident">entry</span>.<span class="ident">into_mut</span>(),
            <span class="ident">Vacant</span>(<span class="ident">entry</span>) <span class="op">=&gt;</span> <span class="ident">entry</span>.<span class="ident">insert</span>(<span class="ident">Default</span>::<span class="ident">default</span>()),
        }
    }

}

<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="ident">Ord</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">VacantEntry</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="doccomment">/// Gets a reference to the key that would be used when inserting a value</span>
    <span class="doccomment">/// through the VacantEntry.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">/// assert_eq!(map.entry(&quot;poneyland&quot;).key(), &amp;&quot;poneyland&quot;);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;map_entry_keys&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.10.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">key</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="ident">K</span> {
        <span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">key</span>
    }

    <span class="doccomment">/// Take ownership of the key.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">/// use std::collections::btree_map::Entry;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// if let Entry::Vacant(v) = map.entry(&quot;poneyland&quot;) {</span>
    <span class="doccomment">///     v.into_key();</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;map_entry_recover_keys2&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.12.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">into_key</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">K</span> {
        <span class="self">self</span>.<span class="ident">key</span>
    }

    <span class="doccomment">/// Sets the value of the entry with the `VacantEntry`&#39;s key,</span>
    <span class="doccomment">/// and returns a mutable reference to it.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut count: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// // count the number of occurrences of letters in the vec</span>
    <span class="doccomment">/// for x in vec![&quot;a&quot;,&quot;b&quot;,&quot;a&quot;,&quot;c&quot;,&quot;a&quot;,&quot;b&quot;] {</span>
    <span class="doccomment">///     *count.entry(x).or_insert(0) += 1;</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(count[&quot;a&quot;], 3);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">insert</span>(<span class="self">self</span>, <span class="ident">value</span>: <span class="ident">V</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span> {
        <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">length</span> <span class="op">+=</span> <span class="number">1</span>;

        <span class="kw">let</span> <span class="ident">out_ptr</span>;

        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">ins_k</span>;
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">ins_v</span>;
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">ins_edge</span>;

        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_parent</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">handle</span>.<span class="ident">insert</span>(<span class="self">self</span>.<span class="ident">key</span>, <span class="ident">value</span>) {
            (<span class="ident">Fit</span>(<span class="ident">handle</span>), <span class="kw">_</span>) <span class="op">=&gt;</span> <span class="kw">return</span> <span class="ident">handle</span>.<span class="ident">into_kv_mut</span>().<span class="number">1</span>,
            (<span class="ident">Split</span>(<span class="ident">left</span>, <span class="ident">k</span>, <span class="ident">v</span>, <span class="ident">right</span>), <span class="ident">ptr</span>) <span class="op">=&gt;</span> {
                <span class="ident">ins_k</span> <span class="op">=</span> <span class="ident">k</span>;
                <span class="ident">ins_v</span> <span class="op">=</span> <span class="ident">v</span>;
                <span class="ident">ins_edge</span> <span class="op">=</span> <span class="ident">right</span>;
                <span class="ident">out_ptr</span> <span class="op">=</span> <span class="ident">ptr</span>;
                <span class="ident">left</span>.<span class="ident">ascend</span>().<span class="ident">map_err</span>(<span class="op">|</span><span class="ident">n</span><span class="op">|</span> <span class="ident">n</span>.<span class="ident">into_root_mut</span>())
            }
        };

        <span class="kw">loop</span> {
            <span class="kw">match</span> <span class="ident">cur_parent</span> {
                <span class="prelude-val">Ok</span>(<span class="ident">parent</span>) <span class="op">=&gt;</span> {
                    <span class="kw">match</span> <span class="ident">parent</span>.<span class="ident">insert</span>(<span class="ident">ins_k</span>, <span class="ident">ins_v</span>, <span class="ident">ins_edge</span>) {
                        <span class="ident">Fit</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> <span class="kw">return</span> <span class="kw">unsafe</span> { <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="ident">out_ptr</span> },
                        <span class="ident">Split</span>(<span class="ident">left</span>, <span class="ident">k</span>, <span class="ident">v</span>, <span class="ident">right</span>) <span class="op">=&gt;</span> {
                            <span class="ident">ins_k</span> <span class="op">=</span> <span class="ident">k</span>;
                            <span class="ident">ins_v</span> <span class="op">=</span> <span class="ident">v</span>;
                            <span class="ident">ins_edge</span> <span class="op">=</span> <span class="ident">right</span>;
                            <span class="ident">cur_parent</span> <span class="op">=</span> <span class="ident">left</span>.<span class="ident">ascend</span>().<span class="ident">map_err</span>(<span class="op">|</span><span class="ident">n</span><span class="op">|</span> <span class="ident">n</span>.<span class="ident">into_root_mut</span>());
                        }
                    }
                }
                <span class="prelude-val">Err</span>(<span class="ident">root</span>) <span class="op">=&gt;</span> {
                    <span class="ident">root</span>.<span class="ident">push_level</span>().<span class="ident">push</span>(<span class="ident">ins_k</span>, <span class="ident">ins_v</span>, <span class="ident">ins_edge</span>);
                    <span class="kw">return</span> <span class="kw">unsafe</span> { <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="ident">out_ptr</span> };
                }
            }
        }
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>: <span class="ident">Ord</span>, <span class="ident">V</span><span class="op">&gt;</span> <span class="ident">OccupiedEntry</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="doccomment">/// Gets a reference to the key in the entry.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">/// map.entry(&quot;poneyland&quot;).or_insert(12);</span>
    <span class="doccomment">/// assert_eq!(map.entry(&quot;poneyland&quot;).key(), &amp;&quot;poneyland&quot;);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;map_entry_keys&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.10.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">key</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="ident">K</span> {
        <span class="self">self</span>.<span class="ident">handle</span>.<span class="ident">reborrow</span>().<span class="ident">into_kv</span>().<span class="number">0</span>
    }

    <span class="doccomment">/// Take ownership of the key and value from the map.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">/// use std::collections::btree_map::Entry;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">/// map.entry(&quot;poneyland&quot;).or_insert(12);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// if let Entry::Occupied(o) = map.entry(&quot;poneyland&quot;) {</span>
    <span class="doccomment">///     // We delete the entry from the map.</span>
    <span class="doccomment">///     o.remove_entry();</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// // If now try to get the value, it will panic:</span>
    <span class="doccomment">/// // println!(&quot;{}&quot;, map[&quot;poneyland&quot;]);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;map_entry_recover_keys2&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.12.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">remove_entry</span>(<span class="self">self</span>) <span class="op">-&gt;</span> (<span class="ident">K</span>, <span class="ident">V</span>) {
        <span class="self">self</span>.<span class="ident">remove_kv</span>()
    }

    <span class="doccomment">/// Gets a reference to the value in the entry.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">/// use std::collections::btree_map::Entry;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">/// map.entry(&quot;poneyland&quot;).or_insert(12);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// if let Entry::Occupied(o) = map.entry(&quot;poneyland&quot;) {</span>
    <span class="doccomment">///     assert_eq!(o.get(), &amp;12);</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="ident">V</span> {
        <span class="self">self</span>.<span class="ident">handle</span>.<span class="ident">reborrow</span>().<span class="ident">into_kv</span>().<span class="number">1</span>
    }

    <span class="doccomment">/// Gets a mutable reference to the value in the entry.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// If you need a reference to the `OccupiedEntry` which may outlive the</span>
    <span class="doccomment">/// destruction of the `Entry` value, see [`into_mut`].</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// [`into_mut`]: #method.into_mut</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">/// use std::collections::btree_map::Entry;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">/// map.entry(&quot;poneyland&quot;).or_insert(12);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(map[&quot;poneyland&quot;], 12);</span>
    <span class="doccomment">/// if let Entry::Occupied(mut o) = map.entry(&quot;poneyland&quot;) {</span>
    <span class="doccomment">///     *o.get_mut() += 10;</span>
    <span class="doccomment">///     assert_eq!(*o.get(), 22);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">///     // We can use the same Entry multiple times.</span>
    <span class="doccomment">///     *o.get_mut() += 2;</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// assert_eq!(map[&quot;poneyland&quot;], 24);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get_mut</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">V</span> {
        <span class="self">self</span>.<span class="ident">handle</span>.<span class="ident">kv_mut</span>().<span class="number">1</span>
    }

    <span class="doccomment">/// Converts the entry into a mutable reference to its value.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// If you need multiple references to the `OccupiedEntry`, see [`get_mut`].</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// [`get_mut`]: #method.get_mut</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">/// use std::collections::btree_map::Entry;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">/// map.entry(&quot;poneyland&quot;).or_insert(12);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(map[&quot;poneyland&quot;], 12);</span>
    <span class="doccomment">/// if let Entry::Occupied(o) = map.entry(&quot;poneyland&quot;) {</span>
    <span class="doccomment">///     *o.into_mut() += 10;</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// assert_eq!(map[&quot;poneyland&quot;], 22);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">into_mut</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">V</span> {
        <span class="self">self</span>.<span class="ident">handle</span>.<span class="ident">into_kv_mut</span>().<span class="number">1</span>
    }

    <span class="doccomment">/// Sets the value of the entry with the `OccupiedEntry`&#39;s key,</span>
    <span class="doccomment">/// and returns the entry&#39;s old value.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">/// use std::collections::btree_map::Entry;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">/// map.entry(&quot;poneyland&quot;).or_insert(12);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// if let Entry::Occupied(mut o) = map.entry(&quot;poneyland&quot;) {</span>
    <span class="doccomment">///     assert_eq!(o.insert(15), 12);</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// assert_eq!(map[&quot;poneyland&quot;], 15);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">insert</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">value</span>: <span class="ident">V</span>) <span class="op">-&gt;</span> <span class="ident">V</span> {
        <span class="ident">mem</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">get_mut</span>(), <span class="ident">value</span>)
    }

    <span class="doccomment">/// Takes the value of the entry out of the map, and returns it.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use std::collections::BTreeMap;</span>
    <span class="doccomment">/// use std::collections::btree_map::Entry;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut map: BTreeMap&lt;&amp;str, usize&gt; = BTreeMap::new();</span>
    <span class="doccomment">/// map.entry(&quot;poneyland&quot;).or_insert(12);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// if let Entry::Occupied(o) = map.entry(&quot;poneyland&quot;) {</span>
    <span class="doccomment">///     assert_eq!(o.remove(), 12);</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// // If we try to get &quot;poneyland&quot;&#39;s value, it&#39;ll panic:</span>
    <span class="doccomment">/// // println!(&quot;{}&quot;, map[&quot;poneyland&quot;]);</span>
    <span class="doccomment">/// ```</span>
    <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;rust1&quot;</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">&quot;1.0.0&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">remove</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">V</span> {
        <span class="self">self</span>.<span class="ident">remove_kv</span>().<span class="number">1</span>
    }

    <span class="kw">fn</span> <span class="ident">remove_kv</span>(<span class="self">self</span>) <span class="op">-&gt;</span> (<span class="ident">K</span>, <span class="ident">V</span>) {
        <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">length</span> <span class="op">-=</span> <span class="number">1</span>;

        <span class="kw">let</span> (<span class="ident">small_leaf</span>, <span class="ident">old_key</span>, <span class="ident">old_val</span>) <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">handle</span>.<span class="ident">force</span>() {
            <span class="ident">Leaf</span>(<span class="ident">leaf</span>) <span class="op">=&gt;</span> {
                <span class="kw">let</span> (<span class="ident">hole</span>, <span class="ident">old_key</span>, <span class="ident">old_val</span>) <span class="op">=</span> <span class="ident">leaf</span>.<span class="ident">remove</span>();
                (<span class="ident">hole</span>.<span class="ident">into_node</span>(), <span class="ident">old_key</span>, <span class="ident">old_val</span>)
            }
            <span class="ident">Internal</span>(<span class="kw-2">mut</span> <span class="ident">internal</span>) <span class="op">=&gt;</span> {
                <span class="kw">let</span> <span class="ident">key_loc</span> <span class="op">=</span> <span class="ident">internal</span>.<span class="ident">kv_mut</span>().<span class="number">0</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">K</span>;
                <span class="kw">let</span> <span class="ident">val_loc</span> <span class="op">=</span> <span class="ident">internal</span>.<span class="ident">kv_mut</span>().<span class="number">1</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">V</span>;

                <span class="kw">let</span> <span class="ident">to_remove</span> <span class="op">=</span> <span class="ident">first_leaf_edge</span>(<span class="ident">internal</span>.<span class="ident">right_edge</span>().<span class="ident">descend</span>()).<span class="ident">right_kv</span>().<span class="ident">ok</span>();
                <span class="kw">let</span> <span class="ident">to_remove</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">unwrap_unchecked</span>(<span class="ident">to_remove</span>) };

                <span class="kw">let</span> (<span class="ident">hole</span>, <span class="ident">key</span>, <span class="ident">val</span>) <span class="op">=</span> <span class="ident">to_remove</span>.<span class="ident">remove</span>();

                <span class="kw">let</span> <span class="ident">old_key</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">mem</span>::<span class="ident">replace</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="ident">key_loc</span>, <span class="ident">key</span>) };
                <span class="kw">let</span> <span class="ident">old_val</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">mem</span>::<span class="ident">replace</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="ident">val_loc</span>, <span class="ident">val</span>) };

                (<span class="ident">hole</span>.<span class="ident">into_node</span>(), <span class="ident">old_key</span>, <span class="ident">old_val</span>)
            }
        };

        <span class="comment">// Handle underflow</span>
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_node</span> <span class="op">=</span> <span class="ident">small_leaf</span>.<span class="ident">forget_type</span>();
        <span class="kw">while</span> <span class="ident">cur_node</span>.<span class="ident">len</span>() <span class="op">&lt;</span> <span class="ident">node</span>::<span class="ident">CAPACITY</span> <span class="op">/</span> <span class="number">2</span> {
            <span class="kw">match</span> <span class="ident">handle_underfull_node</span>(<span class="ident">cur_node</span>) {
                <span class="ident">AtRoot</span> <span class="op">=&gt;</span> <span class="kw">break</span>,
                <span class="ident">EmptyParent</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> <span class="macro">unreachable</span><span class="macro">!</span>(),
                <span class="ident">Merged</span>(<span class="ident">parent</span>) <span class="op">=&gt;</span> {
                    <span class="kw">if</span> <span class="ident">parent</span>.<span class="ident">len</span>() <span class="op">==</span> <span class="number">0</span> {
                        <span class="comment">// We must be at the root</span>
                        <span class="ident">parent</span>.<span class="ident">into_root_mut</span>().<span class="ident">pop_level</span>();
                        <span class="kw">break</span>;
                    } <span class="kw">else</span> {
                        <span class="ident">cur_node</span> <span class="op">=</span> <span class="ident">parent</span>.<span class="ident">forget_type</span>();
                    }
                }
                <span class="ident">Stole</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> <span class="kw">break</span>,
            }
        }

        (<span class="ident">old_key</span>, <span class="ident">old_val</span>)
    }
}

<span class="kw">enum</span> <span class="ident">UnderflowResult</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="ident">AtRoot</span>,
    <span class="ident">EmptyParent</span>(<span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Mut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Internal</span><span class="op">&gt;</span>),
    <span class="ident">Merged</span>(<span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Mut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Internal</span><span class="op">&gt;</span>),
    <span class="ident">Stole</span>(<span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Mut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">Internal</span><span class="op">&gt;</span>),
}

<span class="kw">fn</span> <span class="ident">handle_underfull_node</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span>(<span class="ident">node</span>: <span class="ident">NodeRef</span><span class="op">&lt;</span><span class="ident">marker</span>::<span class="ident">Mut</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>, <span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">marker</span>::<span class="ident">LeafOrInternal</span><span class="op">&gt;</span>)
                                   <span class="op">-&gt;</span> <span class="ident">UnderflowResult</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">K</span>, <span class="ident">V</span><span class="op">&gt;</span> {
    <span class="kw">let</span> <span class="ident">parent</span> <span class="op">=</span> <span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Ok</span>(<span class="ident">parent</span>) <span class="op">=</span> <span class="ident">node</span>.<span class="ident">ascend</span>() {
        <span class="ident">parent</span>
    } <span class="kw">else</span> {
        <span class="kw">return</span> <span class="ident">AtRoot</span>;
    };

    <span class="kw">let</span> (<span class="ident">is_left</span>, <span class="kw-2">mut</span> <span class="ident">handle</span>) <span class="op">=</span> <span class="kw">match</span> <span class="ident">parent</span>.<span class="ident">left_kv</span>() {
        <span class="prelude-val">Ok</span>(<span class="ident">left</span>) <span class="op">=&gt;</span> (<span class="bool-val">true</span>, <span class="ident">left</span>),
        <span class="prelude-val">Err</span>(<span class="ident">parent</span>) <span class="op">=&gt;</span> {
            <span class="kw">match</span> <span class="ident">parent</span>.<span class="ident">right_kv</span>() {
                <span class="prelude-val">Ok</span>(<span class="ident">right</span>) <span class="op">=&gt;</span> (<span class="bool-val">false</span>, <span class="ident">right</span>),
                <span class="prelude-val">Err</span>(<span class="ident">parent</span>) <span class="op">=&gt;</span> {
                    <span class="kw">return</span> <span class="ident">EmptyParent</span>(<span class="ident">parent</span>.<span class="ident">into_node</span>());
                }
            }
        }
    };

    <span class="kw">if</span> <span class="ident">handle</span>.<span class="ident">can_merge</span>() {
        <span class="ident">Merged</span>(<span class="ident">handle</span>.<span class="ident">merge</span>().<span class="ident">into_node</span>())
    } <span class="kw">else</span> {
        <span class="kw">if</span> <span class="ident">is_left</span> {
            <span class="ident">handle</span>.<span class="ident">steal_left</span>();
        } <span class="kw">else</span> {
            <span class="ident">handle</span>.<span class="ident">steal_right</span>();
        }
        <span class="ident">Stole</span>(<span class="ident">handle</span>.<span class="ident">into_node</span>())
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">K</span>: <span class="ident">Ord</span>, <span class="ident">V</span>, <span class="ident">I</span>: <span class="ident">Iterator</span><span class="op">&lt;</span><span class="ident">Item</span> <span class="op">=</span> (<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;&gt;</span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">MergeIter</span><span class="op">&lt;</span><span class="ident">K</span>, <span class="ident">V</span>, <span class="ident">I</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> (<span class="ident">K</span>, <span class="ident">V</span>);

    <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span>(<span class="ident">K</span>, <span class="ident">V</span>)<span class="op">&gt;</span> {
        <span class="kw">let</span> <span class="ident">res</span> <span class="op">=</span> <span class="kw">match</span> (<span class="self">self</span>.<span class="ident">left</span>.<span class="ident">peek</span>(), <span class="self">self</span>.<span class="ident">right</span>.<span class="ident">peek</span>()) {
            (<span class="prelude-val">Some</span>(<span class="kw-2">&amp;</span>(<span class="kw-2">ref</span> <span class="ident">left_key</span>, <span class="kw">_</span>)), <span class="prelude-val">Some</span>(<span class="kw-2">&amp;</span>(<span class="kw-2">ref</span> <span class="ident">right_key</span>, <span class="kw">_</span>))) <span class="op">=&gt;</span> <span class="ident">left_key</span>.<span class="ident">cmp</span>(<span class="ident">right_key</span>),
            (<span class="prelude-val">Some</span>(<span class="kw">_</span>), <span class="prelude-val">None</span>) <span class="op">=&gt;</span> <span class="ident">Ordering</span>::<span class="ident">Less</span>,
            (<span class="prelude-val">None</span>, <span class="prelude-val">Some</span>(<span class="kw">_</span>)) <span class="op">=&gt;</span> <span class="ident">Ordering</span>::<span class="ident">Greater</span>,
            (<span class="prelude-val">None</span>, <span class="prelude-val">None</span>) <span class="op">=&gt;</span> <span class="kw">return</span> <span class="prelude-val">None</span>,
        };

        <span class="comment">// Check which elements comes first and only advance the corresponding iterator.</span>
        <span class="comment">// If two keys are equal, take the value from `right`.</span>
        <span class="kw">match</span> <span class="ident">res</span> {
            <span class="ident">Ordering</span>::<span class="ident">Less</span> <span class="op">=&gt;</span> <span class="self">self</span>.<span class="ident">left</span>.<span class="ident">next</span>(),
            <span class="ident">Ordering</span>::<span class="ident">Greater</span> <span class="op">=&gt;</span> <span class="self">self</span>.<span class="ident">right</span>.<span class="ident">next</span>(),
            <span class="ident">Ordering</span>::<span class="ident">Equal</span> <span class="op">=&gt;</span> {
                <span class="self">self</span>.<span class="ident">left</span>.<span class="ident">next</span>();
                <span class="self">self</span>.<span class="ident">right</span>.<span class="ident">next</span>()
            }
        }
    }
}
</pre>
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