<!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="API documentation for the Rust `VacantEntry` struct in crate `std`."><meta name="keywords" content="rust, rustlang, rust-lang, VacantEntry"><title>std::collections::btree_map::VacantEntry - Rust</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 struct"><!--[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">☰</div><a href='../../../std/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a><p class='location'>Struct VacantEntry</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#methods">Methods</a><div class="sidebar-links"><a href="#method.key">key</a><a href="#method.into_key">into_key</a><a href="#method.insert">insert</a></div><a class="sidebar-title" href="#implementations">Trait Implementations</a><div class="sidebar-links"><a href="#impl-Debug">Debug</a></div><a class="sidebar-title" href="#synthetic-implementations">Auto Trait Implementations</a><div class="sidebar-links"><a href="#impl-Send">Send</a><a href="#impl-Sync">Sync</a></div></div><p class='location'><a href='../../index.html'>std</a>::<wbr><a href='../index.html'>collections</a>::<wbr><a href='index.html'>btree_map</a></p><script>window.sidebarCurrent = {name: 'VacantEntry', ty: 'struct', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></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"><h1 class='fqn'><span class='in-band'>Struct <a href='../../index.html'>std</a>::<wbr><a href='../index.html'>collections</a>::<wbr><a href='index.html'>btree_map</a>::<wbr><a class="struct" href=''>VacantEntry</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version 1.0.0'>1.0.0</span><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../../../src/alloc/btree/map.rs.html#461-468' title='goto source code'>[src]</a></span></h1><div class="docblock type-decl"><pre class='rust struct'>pub struct VacantEntry<'a, K, V> <span class="where fmt-newline">where<br> K: 'a,<br> V: 'a, </span> { /* fields omitted */ }</pre></div><div class='docblock'><p>A view into a vacant entry in a <code>BTreeMap</code>.
It is part of the <a href="enum.Entry.html"><code>Entry</code></a> enum.</p>
</div>
<h2 id='methods' class='small-section-header'>
Methods<a href='#methods' class='anchor'></a>
</h2>
<h3 id='impl' class='impl'><span class='in-band'><table class='table-display'><tbody><tr><td><code>impl<'a, K, V> <a class="struct" href="../../../std/collections/btree_map/struct.VacantEntry.html" title="struct std::collections::btree_map::VacantEntry">VacantEntry</a><'a, K, V> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/cmp/trait.Ord.html" title="trait std::cmp::Ord">Ord</a>, </span></code><a href='#impl' class='anchor'></a></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/alloc/btree/map.rs.html#2212-2306' title='goto source code'>[src]</a></span></td></tr></tbody></table></h3><div class='impl-items'><h4 id='method.key' class="method"><div class="important-traits"><div class='tooltip'>ⓘ<span class='tooltiptext'>Important traits for <a class="primitive" href="../../primitive.reference.html">&'a mut </a>I</span></div><div class="content hidden"><h3 class="important">Important traits for <a class="primitive" href="../../primitive.reference.html">&'a mut </a>I</h3><code class="content"><span class="where fmt-newline">impl<'a, I> <a class="trait" href="../../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a> for <a class="primitive" href="../../primitive.reference.html">&'a mut </a>I <span class="where fmt-newline">where<br> I: <a class="trait" href="../../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a> + ?<a class="trait" href="../../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>, </span></span><span class="where fmt-newline"> type <a href='../../../std/iter/trait.Iterator.html#associatedtype.Item' class="type">Item</a> = <I as <a class="trait" href="../../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a>>::<a class="type" href="../../../std/iter/trait.Iterator.html#associatedtype.Item" title="type std::iter::Iterator::Item">Item</a>;</span><span class="where fmt-newline">impl<'a, R: <a class="trait" href="../../../std/io/trait.Read.html" title="trait std::io::Read">Read</a> + ?<a class="trait" href="../../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>> <a class="trait" href="../../../std/io/trait.Read.html" title="trait std::io::Read">Read</a> for <a class="primitive" href="../../primitive.reference.html">&'a mut </a>R</span><span class="where fmt-newline">impl<'a, W: <a class="trait" href="../../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> + ?<a class="trait" href="../../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>> <a class="trait" href="../../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> for <a class="primitive" href="../../primitive.reference.html">&'a mut </a>W</span></code></div></div><span id='key.v' class='invisible'><table class='table-display'><tbody><tr><td><code>pub fn <a href='#method.key' class='fnname'>key</a>(&self) -> <a class="primitive" href="../../primitive.reference.html">&</a>K</code></span></td><td><span class='out-of-band'><div class='ghost'></div><div class='since' title='Stable since Rust version 1.10.0'>1.10.0</div><a class='srclink' href='../../../src/alloc/btree/map.rs.html#2225-2227' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Gets a reference to the key that would be used when inserting a value
through the VacantEntry.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">collections</span>::<span class="ident">BTreeMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span>: <span class="ident">BTreeMap</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">str</span>, <span class="ident">usize</span><span class="op">></span> <span class="op">=</span> <span class="ident">BTreeMap</span>::<span class="ident">new</span>();
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">map</span>.<span class="ident">entry</span>(<span class="string">"poneyland"</span>).<span class="ident">key</span>(), <span class="kw-2">&</span><span class="string">"poneyland"</span>);<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Acollections%3A%3ABTreeMap%3B%0A%0Alet%20mut%20map%3A%20BTreeMap%3C%26str%2C%20usize%3E%20%3D%20BTreeMap%3A%3Anew()%3B%0Aassert_eq!(map.entry(%22poneyland%22).key()%2C%20%26%22poneyland%22)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.into_key' class="method"><span id='into_key.v' class='invisible'><table class='table-display'><tbody><tr><td><code>pub fn <a href='#method.into_key' class='fnname'>into_key</a>(self) -> K</code></span></td><td><span class='out-of-band'><div class='ghost'></div><div class='since' title='Stable since Rust version 1.12.0'>1.12.0</div><a class='srclink' href='../../../src/alloc/btree/map.rs.html#2244-2246' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Take ownership of the key.</p>
<h1 id="examples-1" class="section-header"><a href="#examples-1">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">collections</span>::<span class="ident">BTreeMap</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">collections</span>::<span class="ident">btree_map</span>::<span class="ident">Entry</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">map</span>: <span class="ident">BTreeMap</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">str</span>, <span class="ident">usize</span><span class="op">></span> <span class="op">=</span> <span class="ident">BTreeMap</span>::<span class="ident">new</span>();
<span class="kw">if</span> <span class="kw">let</span> <span class="ident">Entry</span>::<span class="ident">Vacant</span>(<span class="ident">v</span>) <span class="op">=</span> <span class="ident">map</span>.<span class="ident">entry</span>(<span class="string">"poneyland"</span>) {
<span class="ident">v</span>.<span class="ident">into_key</span>();
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Acollections%3A%3ABTreeMap%3B%0Ause%20std%3A%3Acollections%3A%3Abtree_map%3A%3AEntry%3B%0A%0Alet%20mut%20map%3A%20BTreeMap%3C%26str%2C%20usize%3E%20%3D%20BTreeMap%3A%3Anew()%3B%0A%0Aif%20let%20Entry%3A%3AVacant(v)%20%3D%20map.entry(%22poneyland%22)%20%7B%0A%20%20%20%20v.into_key()%3B%0A%7D%0A%7D">Run</a></pre>
</div><h4 id='method.insert' class="method"><div class="important-traits"><div class='tooltip'>ⓘ<span class='tooltiptext'>Important traits for <a class="primitive" href="../../primitive.reference.html">&'a mut </a>I</span></div><div class="content hidden"><h3 class="important">Important traits for <a class="primitive" href="../../primitive.reference.html">&'a mut </a>I</h3><code class="content"><span class="where fmt-newline">impl<'a, I> <a class="trait" href="../../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a> for <a class="primitive" href="../../primitive.reference.html">&'a mut </a>I <span class="where fmt-newline">where<br> I: <a class="trait" href="../../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a> + ?<a class="trait" href="../../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>, </span></span><span class="where fmt-newline"> type <a href='../../../std/iter/trait.Iterator.html#associatedtype.Item' class="type">Item</a> = <I as <a class="trait" href="../../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a>>::<a class="type" href="../../../std/iter/trait.Iterator.html#associatedtype.Item" title="type std::iter::Iterator::Item">Item</a>;</span><span class="where fmt-newline">impl<'a, R: <a class="trait" href="../../../std/io/trait.Read.html" title="trait std::io::Read">Read</a> + ?<a class="trait" href="../../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>> <a class="trait" href="../../../std/io/trait.Read.html" title="trait std::io::Read">Read</a> for <a class="primitive" href="../../primitive.reference.html">&'a mut </a>R</span><span class="where fmt-newline">impl<'a, W: <a class="trait" href="../../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> + ?<a class="trait" href="../../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>> <a class="trait" href="../../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> for <a class="primitive" href="../../primitive.reference.html">&'a mut </a>W</span></code></div></div><span id='insert.v' class='invisible'><table class='table-display'><tbody><tr><td><code>pub fn <a href='#method.insert' class='fnname'>insert</a>(self, value: V) -> <a class="primitive" href="../../primitive.reference.html">&'a mut </a>V</code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/alloc/btree/map.rs.html#2266-2305' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Sets the value of the entry with the <code>VacantEntry</code>'s key,
and returns a mutable reference to it.</p>
<h1 id="examples-2" class="section-header"><a href="#examples-2">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">collections</span>::<span class="ident">BTreeMap</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">count</span>: <span class="ident">BTreeMap</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">str</span>, <span class="ident">usize</span><span class="op">></span> <span class="op">=</span> <span class="ident">BTreeMap</span>::<span class="ident">new</span>();
<span class="comment">// count the number of occurrences of letters in the vec</span>
<span class="kw">for</span> <span class="ident">x</span> <span class="kw">in</span> <span class="macro">vec</span><span class="macro">!</span>[<span class="string">"a"</span>,<span class="string">"b"</span>,<span class="string">"a"</span>,<span class="string">"c"</span>,<span class="string">"a"</span>,<span class="string">"b"</span>] {
<span class="kw-2">*</span><span class="ident">count</span>.<span class="ident">entry</span>(<span class="ident">x</span>).<span class="ident">or_insert</span>(<span class="number">0</span>) <span class="op">+=</span> <span class="number">1</span>;
}
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">count</span>[<span class="string">"a"</span>], <span class="number">3</span>);<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Acollections%3A%3ABTreeMap%3B%0A%0Alet%20mut%20count%3A%20BTreeMap%3C%26str%2C%20usize%3E%20%3D%20BTreeMap%3A%3Anew()%3B%0A%0A%2F%2F%20count%20the%20number%20of%20occurrences%20of%20letters%20in%20the%20vec%0Afor%20x%20in%20vec!%5B%22a%22%2C%22b%22%2C%22a%22%2C%22c%22%2C%22a%22%2C%22b%22%5D%20%7B%0A%20%20%20%20*count.entry(x).or_insert(0)%20%2B%3D%201%3B%0A%7D%0A%0Aassert_eq!(count%5B%22a%22%5D%2C%203)%3B%0A%7D">Run</a></pre>
</div></div>
<h2 id='implementations' class='small-section-header'>
Trait Implementations<a href='#implementations' class='anchor'></a>
</h2>
<div id='implementations-list'><h3 id='impl-Debug' class='impl'><span class='in-band'><table class='table-display'><tbody><tr><td><code>impl<'a, K, V> <a class="trait" href="../../../std/fmt/trait.Debug.html" title="trait std::fmt::Debug">Debug</a> for <a class="struct" href="../../../std/collections/btree_map/struct.VacantEntry.html" title="struct std::collections::btree_map::VacantEntry">VacantEntry</a><'a, K, V> <span class="where fmt-newline">where<br> K: 'a + <a class="trait" href="../../../std/cmp/trait.Ord.html" title="trait std::cmp::Ord">Ord</a> + <a class="trait" href="../../../std/fmt/trait.Debug.html" title="trait std::fmt::Debug">Debug</a>,<br> V: 'a, </span></code><a href='#impl-Debug' class='anchor'></a></span></td><td><span class='out-of-band'><div class='ghost'></div><div class='since' title='Stable since Rust version 1.12.0'>1.12.0</div><a class='srclink' href='../../../src/alloc/btree/map.rs.html#471-477' title='goto source code'>[src]</a></span></td></tr></tbody></table></h3><div class='impl-items'><h4 id='method.fmt' class="method"><span id='fmt.v' class='invisible'><table class='table-display'><tbody><tr><td><code>fn <a href='../../../std/fmt/trait.Debug.html#tymethod.fmt' class='fnname'>fmt</a>(&self, f: &mut <a class="struct" href="../../../std/fmt/struct.Formatter.html" title="struct std::fmt::Formatter">Formatter</a>) -> <a class="enum" href="../../../std/result/enum.Result.html" title="enum std::result::Result">Result</a><<a class="primitive" href="../../primitive.unit.html">()</a>, <a class="struct" href="../../../std/fmt/struct.Error.html" title="struct std::fmt::Error">Error</a>></code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/alloc/btree/map.rs.html#472-476' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Formats the value using the given formatter. <a href="../../../std/fmt/trait.Debug.html#tymethod.fmt">Read more</a></p>
</div></div></div>
<h2 id='synthetic-implementations' class='small-section-header'>
Auto Trait Implementations<a href='#synthetic-implementations' class='anchor'></a>
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<div id='synthetic-implementations-list'>
<h3 id='impl-Send' class='impl'><span class='in-band'><table class='table-display'><tbody><tr><td><code>impl<'a, K, V> <a class="trait" href="../../../std/marker/trait.Send.html" title="trait std::marker::Send">Send</a> for <a class="struct" href="../../../std/collections/btree_map/struct.VacantEntry.html" title="struct std::collections::btree_map::VacantEntry">VacantEntry</a><'a, K, V> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/marker/trait.Send.html" title="trait std::marker::Send">Send</a>,<br> V: <a class="trait" href="../../../std/marker/trait.Send.html" title="trait std::marker::Send">Send</a>, </span></code><a href='#impl-Send' class='anchor'></a></span></td><td><span class='out-of-band'></span></td></tr></tbody></table></h3><div class='impl-items'></div><h3 id='impl-Sync' class='impl'><span class='in-band'><table class='table-display'><tbody><tr><td><code>impl<'a, K, V> <a class="trait" href="../../../std/marker/trait.Sync.html" title="trait std::marker::Sync">Sync</a> for <a class="struct" href="../../../std/collections/btree_map/struct.VacantEntry.html" title="struct std::collections::btree_map::VacantEntry">VacantEntry</a><'a, K, V> <span class="where fmt-newline">where<br> K: <a class="trait" href="../../../std/marker/trait.Sync.html" title="trait std::marker::Sync">Sync</a>,<br> V: <a class="trait" href="../../../std/marker/trait.Sync.html" title="trait std::marker::Sync">Sync</a>, </span></code><a href='#impl-Sync' class='anchor'></a></span></td><td><span class='out-of-band'></span></td></tr></tbody></table></h3><div class='impl-items'></div></div></section><section id="search" class="content hidden"></section><section class="footer"></section><aside id="help" class="hidden"><div><h1 class="hidden">Help</h1><div class="shortcuts"><h2>Keyboard Shortcuts</h2><dl><dt><kbd>?</kbd></dt><dd>Show this help dialog</dd><dt><kbd>S</kbd></dt><dd>Focus the search field</dd><dt><kbd>↑</kbd></dt><dd>Move up in search results</dd><dt><kbd>↓</kbd></dt><dd>Move down in search results</dd><dt><kbd>↹</kbd></dt><dd>Switch tab</dd><dt><kbd>⏎</kbd></dt><dd>Go to active search result</dd><dt><kbd>+</kbd></dt><dd>Expand all sections</dd><dt><kbd>-</kbd></dt><dd>Collapse all sections</dd></dl></div><div class="infos"><h2>Search Tricks</h2><p>Prefix searches with a type followed by a colon (e.g. <code>fn:</code>) to restrict the search to a given type.</p><p>Accepted types are: <code>fn</code>, <code>mod</code>, <code>struct</code>, <code>enum</code>, <code>trait</code>, <code>type</code>, <code>macro</code>, and <code>const</code>.</p><p>Search functions by type signature (e.g. <code>vec -> usize</code> or <code>* -> vec</code>)</p><p>Search multiple things at once by splitting your query with comma (e.g. <code>str,u8</code> or <code>String,struct:Vec,test</code>)</p></div></div></aside><script>window.rootPath = "../../../";window.currentCrate = "std";</script><script src="../../../aliases.js"></script><script src="../../../main.js"></script><script defer src="../../../search-index.js"></script></body></html>
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