<!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 `AsRef` trait in crate `core`."><meta name="keywords" content="rust, rustlang, rust-lang, AsRef"><title>core::convert::AsRef - 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 trait"><!--[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><p class='location'>Trait AsRef</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#required-methods">Required Methods</a><div class="sidebar-links"><a href="#tymethod.as_ref">as_ref</a></div><a class="sidebar-title" href="#implementors">Implementors</a></div><p class='location'><a href='../index.html'>core</a>::<wbr><a href='index.html'>convert</a></p><script>window.sidebarCurrent = {name: 'AsRef', ty: 'trait', 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'>Trait <a href='../index.html'>core</a>::<wbr><a href='index.html'>convert</a>::<wbr><a class="trait" href=''>AsRef</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/core/convert.rs.html#106-110' title='goto source code'>[src]</a></span></h1><div class="docblock type-decl"><pre class='rust trait'>pub trait AsRef<T: ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> {
fn <a href='#tymethod.as_ref' class='fnname'>as_ref</a>(&self) -> &T;
}</pre></div><div class='docblock'><p>A cheap reference-to-reference conversion. Used to convert a value to a
reference value within generic code.</p>
<p><code>AsRef</code> is very similar to, but serves a slightly different purpose than,
<a href="../../std/borrow/trait.Borrow.html"><code>Borrow</code></a>.</p>
<p><code>AsRef</code> is to be used when wishing to convert to a reference of another
type.
<code>Borrow</code> is more related to the notion of taking the reference. It is
useful when wishing to abstract over the type of reference
(<code>&T</code>, <code>&mut T</code>) or allow both the referenced and owned type to be treated
in the same manner.</p>
<p>The key difference between the two traits is the intention:</p>
<ul>
<li>Use <code>AsRef</code> when goal is to simply convert into a reference</li>
<li>Use <code>Borrow</code> when goal is related to writing code that is agnostic to the
type of borrow and if is reference or value</li>
</ul>
<p>See <a href="../../book/first-edition/borrow-and-asref.html">the book</a> for a more detailed comparison.</p>
<p><strong>Note: this trait must not fail</strong>. If the conversion can fail, use a
dedicated method which returns an <a href="../../std/option/enum.Option.html"><code>Option<T></code></a> or a <a href="../../std/result/enum.Result.html"><code>Result<T, E></code></a>.</p>
<h1 id="generic-implementations" class="section-header"><a href="#generic-implementations">Generic Implementations</a></h1>
<ul>
<li><code>AsRef</code> auto-dereferences if the inner type is a reference or a mutable
reference (e.g.: <code>foo.as_ref()</code> will work the same if <code>foo</code> has type
<code>&mut Foo</code> or <code>&&mut Foo</code>)</li>
</ul>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>Both <a href="../../std/string/struct.String.html"><code>String</code></a> and <code>&str</code> implement <code>AsRef<str></code>:</p>
<pre class="rust rust-example-rendered">
<span class="kw">fn</span> <span class="ident">is_hello</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">AsRef</span><span class="op"><</span><span class="ident">str</span><span class="op">>></span>(<span class="ident">s</span>: <span class="ident">T</span>) {
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="string">"hello"</span>, <span class="ident">s</span>.<span class="ident">as_ref</span>());
}
<span class="kw">let</span> <span class="ident">s</span> <span class="op">=</span> <span class="string">"hello"</span>;
<span class="ident">is_hello</span>(<span class="ident">s</span>);
<span class="kw">let</span> <span class="ident">s</span> <span class="op">=</span> <span class="string">"hello"</span>.<span class="ident">to_string</span>();
<span class="ident">is_hello</span>(<span class="ident">s</span>);<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Afn%20is_hello%3CT%3A%20AsRef%3Cstr%3E%3E(s%3A%20T)%20%7B%0A%20%20%20assert_eq!(%22hello%22%2C%20s.as_ref())%3B%0A%7D%0A%0Alet%20s%20%3D%20%22hello%22%3B%0Ais_hello(s)%3B%0A%0Alet%20s%20%3D%20%22hello%22.to_string()%3B%0Ais_hello(s)%3B%0A%7D">Run</a></pre>
</div>
<h2 id='required-methods' class='small-section-header'>
Required Methods<a href='#required-methods' class='anchor'></a>
</h2>
<div class='methods'>
<h3 id='tymethod.as_ref' class='method'><span id='as_ref.v' class='invisible'><code>fn <a href='#tymethod.as_ref' class='fnname'>as_ref</a>(&self) -> &T</code></span></h3><div class='docblock'><p>Performs the conversion.</p>
</div></div>
<h2 id='implementors' class='small-section-header'>
Implementors<a href='#implementors' class='anchor'></a>
</h2>
<ul class='item-list' id='implementors-list'>
<li><table class='table-display'><tbody><tr><td><code>impl<'a, T: ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>, U: ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> AsRef<U> for &'a T <span class="where fmt-newline">where<br> T: <a class="trait" href="../../core/convert/trait.AsRef.html" title="trait core::convert::AsRef">AsRef</a><U>, </span></code><td><div class='out-of-band'><a class='srclink' href='../../src/core/convert.rs.html#350-355' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<'a, T: ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>, U: ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> AsRef<U> for &'a mut T <span class="where fmt-newline">where<br> T: <a class="trait" href="../../core/convert/trait.AsRef.html" title="trait core::convert::AsRef">AsRef</a><U>, </span></code><td><div class='out-of-band'><a class='srclink' href='../../src/core/convert.rs.html#359-364' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/convert.rs.html#434-438' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl AsRef<str> for str</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/convert.rs.html#448-453' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 0]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 1]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 2]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 3]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 4]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 5]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 6]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 7]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 8]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 9]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 10]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 11]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 12]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 13]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 14]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 15]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 16]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 17]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 18]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 19]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 20]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 21]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 22]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 23]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 24]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 25]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 26]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 27]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 28]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 29]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 30]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 31]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<T> AsRef<[T]> for [T; 32]</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/array.rs.html#122-127' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<'a, T> AsRef<[T]> for <a class="struct" href="../../core/slice/struct.Iter.html" title="struct core::slice::Iter">Iter</a><'a, T></code><td><div class='out-of-band'><a class='srclink' href='../../src/core/slice/mod.rs.html#2682-2686' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl AsRef<[u8]> for str</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/str/mod.rs.html#3865-3870' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
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