<!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 `identity` fn in crate `core`."><meta name="keywords" content="rust, rustlang, rust-lang, identity"><title>core::convert::identity - Rust</title><link rel="stylesheet" type="text/css" href="../../normalize1.35.0.css"><link rel="stylesheet" type="text/css" href="../../rustdoc1.35.0.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark1.35.0.css"><link rel="stylesheet" type="text/css" href="../../light1.35.0.css" id="themeStyle"><script src="../../storage1.35.0.js"></script><noscript><link rel="stylesheet" href="../../noscript1.35.0.css"></noscript><link rel="shortcut icon" href="../../favicon1.35.0.ico"><style type="text/css">#crate-search{background-image:url("../../down-arrow1.35.0.svg");}</style></head><body class="rustdoc fn"><!--[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='../../rust-logo1.35.0.png' alt='logo' width='100'></a><div class="sidebar-elems"><p class='location'><a href='../index.html'>core</a>::<wbr><a href='index.html'>convert</a></p><script>window.sidebarCurrent = {name: 'identity', ty: 'fn', 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="../../brush1.35.0.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme1.35.0.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../../settings.html"><img src="../../wheel1.35.0.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span class='since' title='Stable since Rust version 1.33.0'>1.33.0</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/core/convert.rs.html#99' title='goto source code'>[src]</a></span><span class='in-band'>Function <a href='../index.html'>core</a>::<wbr><a href='index.html'>convert</a>::<wbr><a class="fn" href=''>identity</a></span></h1><pre class='rust fn'>pub const fn identity<T>(x: T) -> T</pre><div class='docblock'><p>An identity function.</p>
<p>Two things are important to note about this function:</p>
<ul>
<li>
<p>It is not always equivalent to a closure like <code>|x| x</code> since the
closure may coerce <code>x</code> into a different type.</p>
</li>
<li>
<p>It moves the input <code>x</code> passed to the function.</p>
</li>
</ul>
<p>While it might seem strange to have a function that just returns back the
input, there are some interesting uses.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>Using <code>identity</code> to do nothing among other interesting functions:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">convert</span>::<span class="ident">identity</span>;
<span class="kw">fn</span> <span class="ident">manipulation</span>(<span class="ident">x</span>: <span class="ident">u32</span>) <span class="op">-></span> <span class="ident">u32</span> {
<span class="comment">// Let's assume that this function does something interesting.</span>
<span class="ident">x</span> <span class="op">+</span> <span class="number">1</span>
}
<span class="kw">let</span> <span class="ident">_arr</span> <span class="op">=</span> <span class="kw-2">&</span>[<span class="ident">identity</span>, <span class="ident">manipulation</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%3Aconvert%3A%3Aidentity%3B%0A%0Afn%20manipulation(x%3A%20u32)%20-%3E%20u32%20%7B%0A%20%20%20%20%2F%2F%20Let's%20assume%20that%20this%20function%20does%20something%20interesting.%0A%20%20%20%20x%20%2B%201%0A%7D%0A%0Alet%20_arr%20%3D%20%26%5Bidentity%2C%20manipulation%5D%3B%0A%7D">Run</a></pre></div>
<p>Using <code>identity</code> to get a function that changes nothing in a conditional:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">convert</span>::<span class="ident">identity</span>;
<span class="kw">let</span> <span class="ident">do_stuff</span> <span class="op">=</span> <span class="kw">if</span> <span class="ident">condition</span> { <span class="ident">manipulation</span> } <span class="kw">else</span> { <span class="ident">identity</span> };
<span class="comment">// do more interesting stuff..</span>
<span class="kw">let</span> <span class="ident">_results</span> <span class="op">=</span> <span class="ident">do_stuff</span>(<span class="number">42</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%3Aconvert%3A%3Aidentity%3B%0A%0Alet%20condition%20%3D%20true%3B%0A%0Afn%20manipulation(x%3A%20u32)%20-%3E%20u32%20%7B%20x%20%2B%201%20%7D%0A%0Alet%20do_stuff%20%3D%20if%20condition%20%7B%20manipulation%20%7D%20else%20%7B%20identity%20%7D%3B%0A%0A%2F%2F%20do%20more%20interesting%20stuff..%0A%0Alet%20_results%20%3D%20do_stuff(42)%3B%0A%7D">Run</a></pre></div>
<p>Using <code>identity</code> to keep the <code>Some</code> variants of an iterator of <code>Option<T></code>:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">convert</span>::<span class="ident">identity</span>;
<span class="kw">let</span> <span class="ident">iter</span> <span class="op">=</span> <span class="macro">vec</span><span class="macro">!</span>[<span class="prelude-val">Some</span>(<span class="number">1</span>), <span class="prelude-val">None</span>, <span class="prelude-val">Some</span>(<span class="number">3</span>)].<span class="ident">into_iter</span>();
<span class="kw">let</span> <span class="ident">filtered</span> <span class="op">=</span> <span class="ident">iter</span>.<span class="ident">filter_map</span>(<span class="ident">identity</span>).<span class="ident">collect</span>::<span class="op"><</span><span class="ident">Vec</span><span class="op"><</span><span class="kw">_</span><span class="op">>></span>();
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="macro">vec</span><span class="macro">!</span>[<span class="number">1</span>, <span class="number">3</span>], <span class="ident">filtered</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%3Aconvert%3A%3Aidentity%3B%0A%0Alet%20iter%20%3D%20vec!%5BSome(1)%2C%20None%2C%20Some(3)%5D.into_iter()%3B%0Alet%20filtered%20%3D%20iter.filter_map(identity).collect%3A%3A%3CVec%3C_%3E%3E()%3B%0Aassert_eq!(vec!%5B1%2C%203%5D%2C%20filtered)%3B%0A%7D">Run</a></pre></div>
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