<!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 `libcore/iter/sources.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>sources.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">☰</div><a href='../../../core/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> <span id="2"> 2</span> <span id="3"> 3</span> <span id="4"> 4</span> <span id="5"> 5</span> <span id="6"> 6</span> <span id="7"> 7</span> <span id="8"> 8</span> <span id="9"> 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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 <LICENSE-APACHE or</span> <span class="comment">// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span> <span class="comment">// <LICENSE-MIT or http://opensource.org/licenses/MIT>, 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">fmt</span>; <span class="kw">use</span> <span class="ident">marker</span>; <span class="kw">use</span> <span class="ident">usize</span>; <span class="kw">use</span> <span class="kw">super</span>::{<span class="ident">FusedIterator</span>, <span class="ident">TrustedLen</span>}; <span class="doccomment">/// An iterator that repeats an element endlessly.</span> <span class="doccomment">///</span> <span class="doccomment">/// This `struct` is created by the [`repeat`] function. See its documentation for more.</span> <span class="doccomment">///</span> <span class="doccomment">/// [`repeat`]: fn.repeat.html</span> <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Debug</span>)]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Repeat</span><span class="op"><</span><span class="ident">A</span><span class="op">></span> { <span class="ident">element</span>: <span class="ident">A</span> } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">A</span>: <span class="ident">Clone</span><span class="op">></span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">Repeat</span><span class="op"><</span><span class="ident">A</span><span class="op">></span> { <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">A</span>; <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">A</span><span class="op">></span> { <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">element</span>.<span class="ident">clone</span>()) } <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">size_hint</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> (<span class="ident">usize</span>, <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span>) { (<span class="ident">usize</span>::<span class="ident">MAX</span>, <span class="prelude-val">None</span>) } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">A</span>: <span class="ident">Clone</span><span class="op">></span> <span class="ident">DoubleEndedIterator</span> <span class="kw">for</span> <span class="ident">Repeat</span><span class="op"><</span><span class="ident">A</span><span class="op">></span> { <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">next_back</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">A</span><span class="op">></span> { <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">element</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">"fused"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.26.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">A</span>: <span class="ident">Clone</span><span class="op">></span> <span class="ident">FusedIterator</span> <span class="kw">for</span> <span class="ident">Repeat</span><span class="op"><</span><span class="ident">A</span><span class="op">></span> {} <span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"trusted_len"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"37572"</span>)]</span> <span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">A</span>: <span class="ident">Clone</span><span class="op">></span> <span class="ident">TrustedLen</span> <span class="kw">for</span> <span class="ident">Repeat</span><span class="op"><</span><span class="ident">A</span><span class="op">></span> {} <span class="doccomment">/// Creates a new iterator that endlessly repeats a single element.</span> <span class="doccomment">///</span> <span class="doccomment">/// The `repeat()` function repeats a single value over and over and over and</span> <span class="doccomment">/// over and over and 🔁.</span> <span class="doccomment">///</span> <span class="doccomment">/// Infinite iterators like `repeat()` are often used with adapters like</span> <span class="doccomment">/// [`take`], in order to make them finite.</span> <span class="doccomment">///</span> <span class="doccomment">/// [`take`]: trait.Iterator.html#method.take</span> <span class="doccomment">///</span> <span class="doccomment">/// If the element type of the iterator you need does not implement `Clone`,</span> <span class="doccomment">/// or if you do not want to keep the repeated element in memory, you can</span> <span class="doccomment">/// instead use the [`repeat_with`] function.</span> <span class="doccomment">///</span> <span class="doccomment">/// [`repeat_with`]: fn.repeat_with.html</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::iter;</span> <span class="doccomment">///</span> <span class="doccomment">/// // the number four 4ever:</span> <span class="doccomment">/// let mut fours = iter::repeat(4);</span> <span class="doccomment">///</span> <span class="doccomment">/// assert_eq!(Some(4), fours.next());</span> <span class="doccomment">/// assert_eq!(Some(4), fours.next());</span> <span class="doccomment">/// assert_eq!(Some(4), fours.next());</span> <span class="doccomment">/// assert_eq!(Some(4), fours.next());</span> <span class="doccomment">/// assert_eq!(Some(4), fours.next());</span> <span class="doccomment">///</span> <span class="doccomment">/// // yup, still four</span> <span class="doccomment">/// assert_eq!(Some(4), fours.next());</span> <span class="doccomment">/// ```</span> <span class="doccomment">///</span> <span class="doccomment">/// Going finite with [`take`]:</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// use std::iter;</span> <span class="doccomment">///</span> <span class="doccomment">/// // that last example was too many fours. Let's only have four fours.</span> <span class="doccomment">/// let mut four_fours = iter::repeat(4).take(4);</span> <span class="doccomment">///</span> <span class="doccomment">/// assert_eq!(Some(4), four_fours.next());</span> <span class="doccomment">/// assert_eq!(Some(4), four_fours.next());</span> <span class="doccomment">/// assert_eq!(Some(4), four_fours.next());</span> <span class="doccomment">/// assert_eq!(Some(4), four_fours.next());</span> <span class="doccomment">///</span> <span class="doccomment">/// // ... and now we're done</span> <span class="doccomment">/// assert_eq!(None, four_fours.next());</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">repeat</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Clone</span><span class="op">></span>(<span class="ident">elt</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">Repeat</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">Repeat</span>{<span class="ident">element</span>: <span class="ident">elt</span>} } <span class="doccomment">/// An iterator that repeats elements of type `A` endlessly by</span> <span class="doccomment">/// applying the provided closure `F: FnMut() -> A`.</span> <span class="doccomment">///</span> <span class="doccomment">/// This `struct` is created by the [`repeat_with`] function.</span> <span class="doccomment">/// See its documentation for more.</span> <span class="doccomment">///</span> <span class="doccomment">/// [`repeat_with`]: fn.repeat_with.html</span> <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Copy</span>, <span class="ident">Clone</span>, <span class="ident">Debug</span>)]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iterator_repeat_with"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">RepeatWith</span><span class="op"><</span><span class="ident">F</span><span class="op">></span> { <span class="ident">repeater</span>: <span class="ident">F</span> } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iterator_repeat_with"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">A</span>, <span class="ident">F</span>: <span class="ident">FnMut</span>() <span class="op">-></span> <span class="ident">A</span><span class="op">></span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">RepeatWith</span><span class="op"><</span><span class="ident">F</span><span class="op">></span> { <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">A</span>; <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">A</span><span class="op">></span> { <span class="prelude-val">Some</span>((<span class="self">self</span>.<span class="ident">repeater</span>)()) } <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="kw">fn</span> <span class="ident">size_hint</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> (<span class="ident">usize</span>, <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span>) { (<span class="ident">usize</span>::<span class="ident">MAX</span>, <span class="prelude-val">None</span>) } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iterator_repeat_with"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">A</span>, <span class="ident">F</span>: <span class="ident">FnMut</span>() <span class="op">-></span> <span class="ident">A</span><span class="op">></span> <span class="ident">FusedIterator</span> <span class="kw">for</span> <span class="ident">RepeatWith</span><span class="op"><</span><span class="ident">F</span><span class="op">></span> {} <span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"trusted_len"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"37572"</span>)]</span> <span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">A</span>, <span class="ident">F</span>: <span class="ident">FnMut</span>() <span class="op">-></span> <span class="ident">A</span><span class="op">></span> <span class="ident">TrustedLen</span> <span class="kw">for</span> <span class="ident">RepeatWith</span><span class="op"><</span><span class="ident">F</span><span class="op">></span> {} <span class="doccomment">/// Creates a new iterator that repeats elements of type `A` endlessly by</span> <span class="doccomment">/// applying the provided closure, the repeater, `F: FnMut() -> A`.</span> <span class="doccomment">///</span> <span class="doccomment">/// The `repeat_with()` function calls the repeater over and over and over and</span> <span class="doccomment">/// over and over and 🔁.</span> <span class="doccomment">///</span> <span class="doccomment">/// Infinite iterators like `repeat_with()` are often used with adapters like</span> <span class="doccomment">/// [`take`], in order to make them finite.</span> <span class="doccomment">///</span> <span class="doccomment">/// [`take`]: trait.Iterator.html#method.take</span> <span class="doccomment">///</span> <span class="doccomment">/// If the element type of the iterator you need implements `Clone`, and</span> <span class="doccomment">/// it is OK to keep the source element in memory, you should instead use</span> <span class="doccomment">/// the [`repeat`] function.</span> <span class="doccomment">///</span> <span class="doccomment">/// [`repeat`]: fn.repeat.html</span> <span class="doccomment">///</span> <span class="doccomment">/// An iterator produced by `repeat_with()` is not a `DoubleEndedIterator`.</span> <span class="doccomment">/// If you need `repeat_with()` to return a `DoubleEndedIterator`,</span> <span class="doccomment">/// please open a GitHub issue explaining your use case.</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::iter;</span> <span class="doccomment">///</span> <span class="doccomment">/// // let's assume we have some value of a type that is not `Clone`</span> <span class="doccomment">/// // or which don't want to have in memory just yet because it is expensive:</span> <span class="doccomment">/// #[derive(PartialEq, Debug)]</span> <span class="doccomment">/// struct Expensive;</span> <span class="doccomment">///</span> <span class="doccomment">/// // a particular value forever:</span> <span class="doccomment">/// let mut things = iter::repeat_with(|| Expensive);</span> <span class="doccomment">///</span> <span class="doccomment">/// assert_eq!(Some(Expensive), things.next());</span> <span class="doccomment">/// assert_eq!(Some(Expensive), things.next());</span> <span class="doccomment">/// assert_eq!(Some(Expensive), things.next());</span> <span class="doccomment">/// assert_eq!(Some(Expensive), things.next());</span> <span class="doccomment">/// assert_eq!(Some(Expensive), things.next());</span> <span class="doccomment">/// ```</span> <span class="doccomment">///</span> <span class="doccomment">/// Using mutation and going finite:</span> <span class="doccomment">///</span> <span class="doccomment">/// ```rust</span> <span class="doccomment">/// use std::iter;</span> <span class="doccomment">///</span> <span class="doccomment">/// // From the zeroth to the third power of two:</span> <span class="doccomment">/// let mut curr = 1;</span> <span class="doccomment">/// let mut pow2 = iter::repeat_with(|| { let tmp = curr; curr *= 2; tmp })</span> <span class="doccomment">/// .take(4);</span> <span class="doccomment">///</span> <span class="doccomment">/// assert_eq!(Some(1), pow2.next());</span> <span class="doccomment">/// assert_eq!(Some(2), pow2.next());</span> <span class="doccomment">/// assert_eq!(Some(4), pow2.next());</span> <span class="doccomment">/// assert_eq!(Some(8), pow2.next());</span> <span class="doccomment">///</span> <span class="doccomment">/// // ... and now we're done</span> <span class="doccomment">/// assert_eq!(None, pow2.next());</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">inline</span>]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iterator_repeat_with"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">repeat_with</span><span class="op"><</span><span class="ident">A</span>, <span class="ident">F</span>: <span class="ident">FnMut</span>() <span class="op">-></span> <span class="ident">A</span><span class="op">></span>(<span class="ident">repeater</span>: <span class="ident">F</span>) <span class="op">-></span> <span class="ident">RepeatWith</span><span class="op"><</span><span class="ident">F</span><span class="op">></span> { <span class="ident">RepeatWith</span> { <span class="ident">repeater</span> } } <span class="doccomment">/// An iterator that yields nothing.</span> <span class="doccomment">///</span> <span class="doccomment">/// This `struct` is created by the [`empty`] function. See its documentation for more.</span> <span class="doccomment">///</span> <span class="doccomment">/// [`empty`]: fn.empty.html</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iter_empty"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">marker</span>::<span class="ident">PhantomData</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>); <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"core_impl_debug"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.9.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> { <span class="ident">f</span>.<span class="ident">pad</span>(<span class="string">"Empty"</span>) } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iter_empty"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">T</span>; <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="prelude-val">None</span> } <span class="kw">fn</span> <span class="ident">size_hint</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> (<span class="ident">usize</span>, <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span>){ (<span class="number">0</span>, <span class="prelude-val">Some</span>(<span class="number">0</span>)) } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iter_empty"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">DoubleEndedIterator</span> <span class="kw">for</span> <span class="ident">Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">next_back</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="prelude-val">None</span> } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iter_empty"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">ExactSizeIterator</span> <span class="kw">for</span> <span class="ident">Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">len</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">usize</span> { <span class="number">0</span> } } <span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"trusted_len"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"37572"</span>)]</span> <span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">TrustedLen</span> <span class="kw">for</span> <span class="ident">Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {} <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"fused"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.26.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">FusedIterator</span> <span class="kw">for</span> <span class="ident">Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {} <span class="comment">// not #[derive] because that adds a Clone bound on T,</span> <span class="comment">// which isn't necessary.</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iter_empty"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">Empty</span>(<span class="ident">marker</span>::<span class="ident">PhantomData</span>) } } <span class="comment">// not #[derive] because that adds a Default bound on T,</span> <span class="comment">// which isn't necessary.</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iter_empty"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-></span> <span class="ident">Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">Empty</span>(<span class="ident">marker</span>::<span class="ident">PhantomData</span>) } } <span class="doccomment">/// Creates an iterator that yields nothing.</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::iter;</span> <span class="doccomment">///</span> <span class="doccomment">/// // this could have been an iterator over i32, but alas, it's just not.</span> <span class="doccomment">/// let mut nope = iter::empty::<i32>();</span> <span class="doccomment">///</span> <span class="doccomment">/// assert_eq!(None, nope.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">"iter_empty"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>() <span class="op">-></span> <span class="ident">Empty</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">Empty</span>(<span class="ident">marker</span>::<span class="ident">PhantomData</span>) } <span class="doccomment">/// An iterator that yields an element exactly once.</span> <span class="doccomment">///</span> <span class="doccomment">/// This `struct` is created by the [`once`] function. See its documentation for more.</span> <span class="doccomment">///</span> <span class="doccomment">/// [`once`]: fn.once.html</span> <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Debug</span>)]</span> <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iter_once"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Once</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">inner</span>: ::<span class="ident">option</span>::<span class="ident">IntoIter</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iter_once"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">Once</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">T</span>; <span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">next</span>() } <span class="kw">fn</span> <span class="ident">size_hint</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> (<span class="ident">usize</span>, <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">usize</span><span class="op">></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">"iter_once"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">DoubleEndedIterator</span> <span class="kw">for</span> <span class="ident">Once</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">next_back</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">next_back</span>() } } <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"iter_once"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">ExactSizeIterator</span> <span class="kw">for</span> <span class="ident">Once</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">len</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></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">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"trusted_len"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"37572"</span>)]</span> <span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">TrustedLen</span> <span class="kw">for</span> <span class="ident">Once</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {} <span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"fused"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.26.0"</span>)]</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">FusedIterator</span> <span class="kw">for</span> <span class="ident">Once</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {} <span class="doccomment">/// Creates an iterator that yields an element exactly once.</span> <span class="doccomment">///</span> <span class="doccomment">/// This is commonly used to adapt a single value into a [`chain`] of other</span> <span class="doccomment">/// kinds of iteration. Maybe you have an iterator that covers almost</span> <span class="doccomment">/// everything, but you need an extra special case. Maybe you have a function</span> <span class="doccomment">/// which works on iterators, but you only need to process one value.</span> <span class="doccomment">///</span> <span class="doccomment">/// [`chain`]: trait.Iterator.html#method.chain</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::iter;</span> <span class="doccomment">///</span> <span class="doccomment">/// // one is the loneliest number</span> <span class="doccomment">/// let mut one = iter::once(1);</span> <span class="doccomment">///</span> <span class="doccomment">/// assert_eq!(Some(1), one.next());</span> <span class="doccomment">///</span> <span class="doccomment">/// // just one, that's all we get</span> <span class="doccomment">/// assert_eq!(None, one.next());</span> <span class="doccomment">/// ```</span> <span class="doccomment">///</span> <span class="doccomment">/// Chaining together with another iterator. Let's say that we want to iterate</span> <span class="doccomment">/// over each file of the `.foo` directory, but also a configuration file,</span> <span class="doccomment">/// `.foorc`:</span> <span class="doccomment">///</span> <span class="doccomment">/// ```no_run</span> <span class="doccomment">/// use std::iter;</span> <span class="doccomment">/// use std::fs;</span> <span class="doccomment">/// use std::path::PathBuf;</span> <span class="doccomment">///</span> <span class="doccomment">/// let dirs = fs::read_dir(".foo").unwrap();</span> <span class="doccomment">///</span> <span class="doccomment">/// // we need to convert from an iterator of DirEntry-s to an iterator of</span> <span class="doccomment">/// // PathBufs, so we use map</span> <span class="doccomment">/// let dirs = dirs.map(|file| file.unwrap().path());</span> <span class="doccomment">///</span> <span class="doccomment">/// // now, our iterator just for our config file</span> <span class="doccomment">/// let config = iter::once(PathBuf::from(".foorc"));</span> <span class="doccomment">///</span> <span class="doccomment">/// // chain the two iterators together into one big iterator</span> <span class="doccomment">/// let files = dirs.chain(config);</span> <span class="doccomment">///</span> <span class="doccomment">/// // this will give us all of the files in .foo as well as .foorc</span> <span class="doccomment">/// for f in files {</span> <span class="doccomment">/// println!("{:?}", f);</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">"iter_once"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.2.0"</span>)]</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">once</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">value</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">Once</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">Once</span> { <span class="ident">inner</span>: <span class="prelude-val">Some</span>(<span class="ident">value</span>).<span class="ident">into_iter</span>() } } </pre> </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 = "core";</script><script src="../../../aliases.js"></script><script src="../../../main.js"></script><script defer src="../../../search-index.js"></script></body></html>