<!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 `discriminant` fn in crate `std`."><meta name="keywords" content="rust, rustlang, rust-lang, discriminant"><title>std::mem::discriminant - 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 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='../../std/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a><div class="sidebar-elems"><p class='location'><a href='../index.html'>std</a>::<wbr><a href='index.html'>mem</a></p><script>window.sidebarCurrent = {name: 'discriminant', 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="../../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'>Function <a href='../index.html'>std</a>::<wbr><a href='index.html'>mem</a>::<wbr><a class="fn" href=''>discriminant</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version 1.21.0'>1.21.0</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/mem.rs.html#910-914' title='goto source code'>[src]</a></span></h1><pre class='rust fn'>pub fn discriminant<T>(v: <a class="primitive" href="../primitive.reference.html">&</a>T) -> <a class="struct" href="../../std/mem/struct.Discriminant.html" title="struct std::mem::Discriminant">Discriminant</a><T></pre><div class='docblock'><p>Returns a value uniquely identifying the enum variant in <code>v</code>.</p>
<p>If <code>T</code> is not an enum, calling this function will not result in undefined behavior, but the
return value is unspecified.</p>
<h1 id="stability" class="section-header"><a href="#stability">Stability</a></h1>
<p>The discriminant of an enum variant may change if the enum definition changes. A discriminant
of some variant will not change between compilations with the same compiler.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>This can be used to compare enums that carry data, while disregarding
the actual data:</p>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">mem</span>;
<span class="kw">enum</span> <span class="ident">Foo</span> { <span class="ident">A</span>(<span class="kw-2">&</span><span class="lifetime">'static</span> <span class="ident">str</span>), <span class="ident">B</span>(<span class="ident">i32</span>), <span class="ident">C</span>(<span class="ident">i32</span>) }
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">mem</span>::<span class="ident">discriminant</span>(<span class="kw-2">&</span><span class="ident">Foo</span>::<span class="ident">A</span>(<span class="string">"bar"</span>)) <span class="op">==</span> <span class="ident">mem</span>::<span class="ident">discriminant</span>(<span class="kw-2">&</span><span class="ident">Foo</span>::<span class="ident">A</span>(<span class="string">"baz"</span>)));
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">mem</span>::<span class="ident">discriminant</span>(<span class="kw-2">&</span><span class="ident">Foo</span>::<span class="ident">B</span>(<span class="number">1</span>)) <span class="op">==</span> <span class="ident">mem</span>::<span class="ident">discriminant</span>(<span class="kw-2">&</span><span class="ident">Foo</span>::<span class="ident">B</span>(<span class="number">2</span>)));
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">mem</span>::<span class="ident">discriminant</span>(<span class="kw-2">&</span><span class="ident">Foo</span>::<span class="ident">B</span>(<span class="number">3</span>)) <span class="op">!=</span> <span class="ident">mem</span>::<span class="ident">discriminant</span>(<span class="kw-2">&</span><span class="ident">Foo</span>::<span class="ident">C</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%3Amem%3B%0A%0Aenum%20Foo%20%7B%20A(%26'static%20str)%2C%20B(i32)%2C%20C(i32)%20%7D%0A%0Aassert!(mem%3A%3Adiscriminant(%26Foo%3A%3AA(%22bar%22))%20%3D%3D%20mem%3A%3Adiscriminant(%26Foo%3A%3AA(%22baz%22)))%3B%0Aassert!(mem%3A%3Adiscriminant(%26Foo%3A%3AB(1))%20%20%20%20%20%3D%3D%20mem%3A%3Adiscriminant(%26Foo%3A%3AB(2)))%3B%0Aassert!(mem%3A%3Adiscriminant(%26Foo%3A%3AB(3))%20%20%20%20%20!%3D%20mem%3A%3Adiscriminant(%26Foo%3A%3AC(3)))%3B%0A%7D">Run</a></pre>
</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>
distrib
>
Mageia
>
6
>
armv7hl
>
media
>
core-updates
>
by-pkgid
>
4e2dbb669434a7691662cb2f0ad38972
>
files
>
13619
