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<!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."><title>try_select in futures_util::future - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-46f98efaafac5295.ttf.woff2,FiraSans-Regular-018c141bf0843ffd.woff2,FiraSans-Medium-8f9a781e4970d388.woff2,SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2,SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../static.files/rustdoc-492a78a4a87dcc01.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="futures_util" data-themes="" data-resource-suffix="" data-rustdoc-version="1.82.0 (f6e511eec 2024-10-15)" data-channel="1.82.0" data-search-js="search-a99f1315e7cc5121.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../static.files/storage-118b08c4c78b968e.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../static.files/main-921df33f47b8780c.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-3b12f09e550e0385.css"></noscript><link rel="alternate icon" type="image/png" href="../../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc fn"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../futures_util/index.html">futures_<wbr>util</a><span class="version">0.3.31</span></h2></div><div class="sidebar-elems"><h2><a href="index.html">In futures_<wbr>util::<wbr>future</a></h2></div></nav><div class="sidebar-resizer"></div><main><div class="width-limiter"><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><h1>Function <a href="../index.html">futures_util</a>::<wbr><a href="index.html">future</a>::<wbr><a class="fn" href="#">try_select</a><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><span class="out-of-band"><a class="src" href="../../src/futures_util/future/try_select.rs.html#53-61">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>&#x2212;</span>]</button></span></div><pre class="rust item-decl"><code>pub fn try_select&lt;A, B&gt;(future1: A, future2: B) -&gt; <a class="struct" href="struct.TrySelect.html" title="struct futures_util::future::TrySelect">TrySelect</a>&lt;A, B&gt; <a href="#" class="tooltip" data-notable-ty="TrySelect&lt;A, B&gt;"></a><div class="where">where
A: <a class="trait" href="trait.TryFuture.html" title="trait futures_util::future::TryFuture">TryFuture</a> + <a class="trait" href="https://doc.rust-lang.org/1.82.0/core/marker/trait.Unpin.html" title="trait core::marker::Unpin">Unpin</a>,
B: <a class="trait" href="trait.TryFuture.html" title="trait futures_util::future::TryFuture">TryFuture</a> + <a class="trait" href="https://doc.rust-lang.org/1.82.0/core/marker/trait.Unpin.html" title="trait core::marker::Unpin">Unpin</a>,</div></code></pre><details class="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 class="doc-anchor" href="#examples">§</a>Examples</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&lt;A, B, E&gt;(a: A, b: B) -&gt; <span class="kw">impl </span>TryFuture&lt;<span class="prelude-val">Ok</span>=(A::Ok, B::Ok), Error=E&gt;
<span class="kw">where </span>A: TryFuture&lt;Error = E&gt; + Unpin + <span class="lifetime">'static</span>,
B: TryFuture&lt;Error = E&gt; + Unpin + <span class="lifetime">'static</span>,
E: <span class="lifetime">'static</span>,
{
future::try_select(a, b).then(|res| -&gt; Box&lt;<span class="kw">dyn </span>Future&lt;Output = <span class="prelude-ty">Result</span>&lt;<span class="kw">_</span>, <span class="kw">_</span>&gt;&gt; + Unpin&gt; {
<span class="kw">match </span>res {
<span class="prelude-val">Ok</span>(Either::Left((x, b))) =&gt; Box::new(b.map_ok(<span class="kw">move </span>|y| (x, y))),
<span class="prelude-val">Ok</span>(Either::Right((y, a))) =&gt; 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>))) =&gt; Box::new(future::err(e)),
<span class="prelude-val">Err</span>(Either::Right((e, <span class="kw">_</span>))) =&gt; Box::new(future::err(e)),
}
})
}</code></pre></div>
</div></details><script type="text/json" id="notable-traits-data">{"TrySelect<A, B>":"<h3>Notable traits for <code><a class=\"struct\" href=\"struct.TrySelect.html\" title=\"struct futures_util::future::TrySelect\">TrySelect</a>&lt;A, B&gt;</code></h3><pre><code><div class=\"where\">impl&lt;A, B&gt; <a class=\"trait\" href=\"https://doc.rust-lang.org/1.82.0/core/future/future/trait.Future.html\" title=\"trait core::future::future::Future\">Future</a> for <a class=\"struct\" href=\"struct.TrySelect.html\" title=\"struct futures_util::future::TrySelect\">TrySelect</a>&lt;A, B&gt;<div class=\"where\">where\n A: <a class=\"trait\" href=\"trait.TryFuture.html\" title=\"trait futures_util::future::TryFuture\">TryFuture</a> + <a class=\"trait\" href=\"https://doc.rust-lang.org/1.82.0/core/marker/trait.Unpin.html\" title=\"trait core::marker::Unpin\">Unpin</a>,\n B: <a class=\"trait\" href=\"trait.TryFuture.html\" title=\"trait futures_util::future::TryFuture\">TryFuture</a> + <a class=\"trait\" href=\"https://doc.rust-lang.org/1.82.0/core/marker/trait.Unpin.html\" title=\"trait core::marker::Unpin\">Unpin</a>,</div></div><div class=\"where\"> type <a href=\"https://doc.rust-lang.org/1.82.0/core/future/future/trait.Future.html#associatedtype.Output\" class=\"associatedtype\">Output</a> = <a class=\"enum\" href=\"https://doc.rust-lang.org/1.82.0/core/result/enum.Result.html\" title=\"enum core::result::Result\">Result</a>&lt;<a class=\"enum\" href=\"enum.Either.html\" title=\"enum futures_util::future::Either\">Either</a>&lt;(&lt;A as <a class=\"trait\" href=\"trait.TryFuture.html\" title=\"trait futures_util::future::TryFuture\">TryFuture</a>&gt;::<a class=\"associatedtype\" href=\"trait.TryFuture.html#associatedtype.Ok\" title=\"type futures_util::future::TryFuture::Ok\">Ok</a>, B), (&lt;B as <a class=\"trait\" href=\"trait.TryFuture.html\" title=\"trait futures_util::future::TryFuture\">TryFuture</a>&gt;::<a class=\"associatedtype\" href=\"trait.TryFuture.html#associatedtype.Ok\" title=\"type futures_util::future::TryFuture::Ok\">Ok</a>, A)&gt;, <a class=\"enum\" href=\"enum.Either.html\" title=\"enum futures_util::future::Either\">Either</a>&lt;(&lt;A as <a class=\"trait\" href=\"trait.TryFuture.html\" title=\"trait futures_util::future::TryFuture\">TryFuture</a>&gt;::<a class=\"associatedtype\" href=\"trait.TryFuture.html#associatedtype.Error\" title=\"type futures_util::future::TryFuture::Error\">Error</a>, B), (&lt;B as <a class=\"trait\" href=\"trait.TryFuture.html\" title=\"trait futures_util::future::TryFuture\">TryFuture</a>&gt;::<a class=\"associatedtype\" href=\"trait.TryFuture.html#associatedtype.Error\" title=\"type futures_util::future::TryFuture::Error\">Error</a>, A)&gt;&gt;;</div>"}</script></section></div></main></body></html>