<!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 `select` macro in crate `std`."><meta name="keywords" content="rust, rustlang, rust-lang, select"><title>std::select - 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 macro"><!--[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></p><script>window.sidebarCurrent = {name: 'select', ty: 'macro', 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'>Macro <a href='index.html'>std</a>::<wbr><a class="macro" href=''>select</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version '></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/std/macros.rs.html#253-267' title='goto source code'>[src]</a></span></h1><div class="docblock type-decl"><pre class="rust macro">
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">select</span> {
(
$(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">name</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">rx</span>:<span class="ident">ident</span>.<span class="macro-nonterminal">$</span><span class="macro-nonterminal">meth</span>:<span class="ident">ident</span>() <span class="op">=></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">code</span>:<span class="ident">expr</span>),<span class="op">+</span>
) <span class="op">=></span> { ... };
}</pre>
</div><div class='stability'><div class='stab unstable'><span class=microscope>🔬</span> This is a nightly-only experimental API. (<code>mpsc_select </code><a href="https://github.com/rust-lang/rust/issues/27800">#27800</a>)</div></div><div class='docblock'><p>A macro to select an event from a number of receivers.</p>
<p>This macro is used to wait for the first event to occur on a number of
receivers. It places no restrictions on the types of receivers given to
this macro, this can be viewed as a heterogeneous select.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="attribute">#![<span class="ident">feature</span>(<span class="ident">mpsc_select</span>)]</span>
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">thread</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">mpsc</span>;
<span class="comment">// two placeholder functions for now</span>
<span class="kw">fn</span> <span class="ident">long_running_thread</span>() {}
<span class="kw">fn</span> <span class="ident">calculate_the_answer</span>() <span class="op">-></span> <span class="ident">u32</span> { <span class="number">42</span> }
<span class="kw">let</span> (<span class="ident">tx1</span>, <span class="ident">rx1</span>) <span class="op">=</span> <span class="ident">mpsc</span>::<span class="ident">channel</span>();
<span class="kw">let</span> (<span class="ident">tx2</span>, <span class="ident">rx2</span>) <span class="op">=</span> <span class="ident">mpsc</span>::<span class="ident">channel</span>();
<span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span><span class="op">||</span> { <span class="ident">long_running_thread</span>(); <span class="ident">tx1</span>.<span class="ident">send</span>(()).<span class="ident">unwrap</span>(); });
<span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span><span class="op">||</span> { <span class="ident">tx2</span>.<span class="ident">send</span>(<span class="ident">calculate_the_answer</span>()).<span class="ident">unwrap</span>(); });
<span class="macro">select</span><span class="macro">!</span> {
<span class="kw">_</span> <span class="op">=</span> <span class="ident">rx1</span>.<span class="ident">recv</span>() <span class="op">=></span> <span class="macro">println</span><span class="macro">!</span>(<span class="string">"the long running thread finished first"</span>),
<span class="ident">answer</span> <span class="op">=</span> <span class="ident">rx2</span>.<span class="ident">recv</span>() <span class="op">=></span> {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"the answer was: {}"</span>, <span class="ident">answer</span>.<span class="ident">unwrap</span>());
}
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0A%23!%5Bfeature(mpsc_select)%5D%0A%0Afn%20main()%20%7B%0Ause%20std%3A%3Athread%3B%0Ause%20std%3A%3Async%3A%3Ampsc%3B%0A%0A%2F%2F%20two%20placeholder%20functions%20for%20now%0Afn%20long_running_thread()%20%7B%7D%0Afn%20calculate_the_answer()%20-%3E%20u32%20%7B%2042%20%7D%0A%0Alet%20(tx1%2C%20rx1)%20%3D%20mpsc%3A%3Achannel()%3B%0Alet%20(tx2%2C%20rx2)%20%3D%20mpsc%3A%3Achannel()%3B%0A%0Athread%3A%3Aspawn(move%7C%7C%20%7B%20long_running_thread()%3B%20tx1.send(()).unwrap()%3B%20%7D)%3B%0Athread%3A%3Aspawn(move%7C%7C%20%7B%20tx2.send(calculate_the_answer()).unwrap()%3B%20%7D)%3B%0A%0Aselect!%20%7B%0A%20%20%20%20_%20%3D%20rx1.recv()%20%3D%3E%20println!(%22the%20long%20running%20thread%20finished%20first%22)%2C%0A%20%20%20%20answer%20%3D%20rx2.recv()%20%3D%3E%20%7B%0A%20%20%20%20%20%20%20%20println!(%22the%20answer%20was%3A%20%7B%7D%22%2C%20answer.unwrap())%3B%0A%20%20%20%20%7D%0A%7D%0Adrop(rx1.recv())%3B%0Adrop(rx2.recv())%3B%0A%7D&version=nightly">Run</a></pre>
<p>For more information about select, see the <code>std::sync::mpsc::Select</code> structure.</p>
</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
>
13573
