| <!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="Waits for either one of two differently-typed futures to complete."><meta name="keywords" content="rust, rustlang, rust-lang, try_select"><title>try_select in futures::prelude::future - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin 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class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../../../futures/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../../../futures/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a><div class="sidebar-elems"><h2><a href="index.html">In futures::prelude::future</a></h2></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Function <a href="../../index.html">futures</a>::<wbr><a href="../index.html">prelude</a>::<wbr><a href="index.html">future</a>::<wbr><a class="fn" href="#">try_select</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../../../src/futures_util/future/try_select.rs.html#53-56">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><pre class="rust fn"><code>pub fn try_select<A, B>(future1: A, future2: B) -> <a class="struct" href="../../future/struct.TrySelect.html" title="struct futures::future::TrySelect">TrySelect</a><A, B><span class="notable-traits"><span class="notable-traits-tooltip">ⓘ<span class="notable-traits-tooltiptext"><span class="docblock"><span class="notable">Notable traits for <a class="struct" href="../../future/struct.TrySelect.html" title="struct futures::future::TrySelect">TrySelect</a><A, B></span><code class="content"><span class="where fmt-newline">impl<A, B> <a class="trait" href="../../future/trait.Future.html" title="trait futures::future::Future">Future</a> for <a class="struct" href="../../future/struct.TrySelect.html" title="struct futures::future::TrySelect">TrySelect</a><A, B><span class="where fmt-newline">where<br> A: Unpin + <a class="trait" href="../../future/trait.TryFuture.html" title="trait futures::future::TryFuture">TryFuture</a>,<br> B: Unpin + <a class="trait" href="../../future/trait.TryFuture.html" title="trait futures::future::TryFuture">TryFuture</a>,</span></span><span class="where fmt-newline"> type <a href="../../future/trait.Future.html#associatedtype.Output" class="associatedtype">Output</a> = Result<<a class="enum" href="../../future/enum.Either.html" title="enum futures::future::Either">Either</a><(<A as <a class="trait" href="../../future/trait.TryFuture.html" title="trait futures::future::TryFuture">TryFuture</a>>::<a class="associatedtype" href="../../future/trait.TryFuture.html#associatedtype.Ok" title="type futures::future::TryFuture::Ok">Ok</a>, B), (<B as <a class="trait" href="../../future/trait.TryFuture.html" title="trait futures::future::TryFuture">TryFuture</a>>::<a class="associatedtype" href="../../future/trait.TryFuture.html#associatedtype.Ok" title="type futures::future::TryFuture::Ok">Ok</a>, A)>, <a class="enum" href="../../future/enum.Either.html" title="enum futures::future::Either">Either</a><(<A as <a class="trait" href="../../future/trait.TryFuture.html" title="trait futures::future::TryFuture">TryFuture</a>>::<a class="associatedtype" href="../../future/trait.TryFuture.html#associatedtype.Error" title="type futures::future::TryFuture::Error">Error</a>, B), (<B as <a class="trait" href="../../future/trait.TryFuture.html" title="trait futures::future::TryFuture">TryFuture</a>>::<a class="associatedtype" href="../../future/trait.TryFuture.html#associatedtype.Error" title="type futures::future::TryFuture::Error">Error</a>, A)>>;</span></code></span></span></span></span><span class="where fmt-newline">where<br> A: <a class="trait" href="../../future/trait.TryFuture.html" title="trait futures::future::TryFuture">TryFuture</a> + Unpin,<br> B: <a class="trait" href="../../future/trait.TryFuture.html" title="trait futures::future::TryFuture">TryFuture</a> + Unpin,</span></code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Waits for either one of two differently-typed futures to complete.</p> |
| <p>This function will return a new future which awaits for either one of both |
| futures to complete. The returned future will finish with both the value |
| resolved and a future representing the completion of the other work.</p> |
| <p>Note that this function consumes the receiving futures and returns a |
| wrapped version of them.</p> |
| <p>Also note that if both this and the second future have the same |
| success/error type you can use the <code>Either::factor_first</code> method to |
| conveniently extract out the value at the end.</p> |
| <h2 id="examples"><a href="#examples">Examples</a></h2> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>futures::future::{<span class="self">self</span>, Either, Future, FutureExt, TryFuture, TryFutureExt}; |
| |
| <span class="comment">// A poor-man's try_join implemented on top of select |
| |
| </span><span class="kw">fn </span>try_join<A, B, E>(a: A, b: B) -> <span class="kw">impl </span>TryFuture<<span class="prelude-val">Ok</span>=(A::Ok, B::Ok), Error=E> |
| <span class="kw">where </span>A: TryFuture<Error = E> + Unpin + <span class="lifetime">'static</span>, |
| B: TryFuture<Error = E> + Unpin + <span class="lifetime">'static</span>, |
| E: <span class="lifetime">'static</span>, |
| { |
| future::try_select(a, b).then(|res| -> Box<<span class="kw">dyn </span>Future<Output = <span class="prelude-ty">Result</span><<span class="kw">_</span>, <span class="kw">_</span>>> + Unpin> { |
| <span class="kw">match </span>res { |
| <span class="prelude-val">Ok</span>(Either::Left((x, b))) => Box::new(b.map_ok(<span class="kw">move </span>|y| (x, y))), |
| <span class="prelude-val">Ok</span>(Either::Right((y, a))) => Box::new(a.map_ok(<span class="kw">move </span>|x| (x, y))), |
| <span class="prelude-val">Err</span>(Either::Left((e, <span class="kw">_</span>))) => Box::new(future::err(e)), |
| <span class="prelude-val">Err</span>(Either::Right((e, <span class="kw">_</span>))) => Box::new(future::err(e)), |
| } |
| }) |
| }</code></pre></div> |
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