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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="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-util-0.3.28/src/future/try_select.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>try_select.rs - source</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 href="../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../../normalize.css"><link rel="stylesheet" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../ayu.css" disabled><link rel="stylesheet" href="../../../dark.css" disabled><link rel="stylesheet" href="../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../storage.js"></script><script defer src="../../../source-script.js"></script><script defer src="../../../source-files.js"></script><script defer src="../../../main.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../../futures_util/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../../futures_util/index.html"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></a><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="example-wrap"><pre class="src-line-numbers"><span id="1">1</span>
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</pre><pre class="rust"><code><span class="kw">use </span><span class="kw">crate</span>::future::{Either, TryFutureExt};
<span class="kw">use </span>core::pin::Pin;
<span class="kw">use </span>futures_core::future::{Future, TryFuture};
<span class="kw">use </span>futures_core::task::{Context, Poll};
<span class="doccomment">/// Future for the [`try_select()`] function.
</span><span class="attribute">#[must_use = <span class="string">&quot;futures do nothing unless you `.await` or poll them&quot;</span>]
#[derive(Debug)]
</span><span class="kw">pub struct </span>TrySelect&lt;A, B&gt; {
inner: <span class="prelude-ty">Option</span>&lt;(A, B)&gt;,
}
<span class="kw">impl</span>&lt;A: Unpin, B: Unpin&gt; Unpin <span class="kw">for </span>TrySelect&lt;A, B&gt; {}
<span class="kw">type </span>EitherOk&lt;A, B&gt; = Either&lt;(&lt;A <span class="kw">as </span>TryFuture&gt;::Ok, B), (&lt;B <span class="kw">as </span>TryFuture&gt;::Ok, A)&gt;;
<span class="kw">type </span>EitherErr&lt;A, B&gt; = Either&lt;(&lt;A <span class="kw">as </span>TryFuture&gt;::Error, B), (&lt;B <span class="kw">as </span>TryFuture&gt;::Error, A)&gt;;
<span class="doccomment">/// Waits for either one of two differently-typed futures to complete.
///
/// 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.
///
/// Note that this function consumes the receiving futures and returns a
/// wrapped version of them.
///
/// Also note that if both this and the second future have the same
/// success/error type you can use the `Either::factor_first` method to
/// conveniently extract out the value at the end.
///
/// # Examples
///
/// ```
/// use futures::future::{self, Either, Future, FutureExt, TryFuture, TryFutureExt};
///
/// // A poor-man&#39;s try_join implemented on top of select
///
/// fn try_join&lt;A, B, E&gt;(a: A, b: B) -&gt; impl TryFuture&lt;Ok=(A::Ok, B::Ok), Error=E&gt;
/// where A: TryFuture&lt;Error = E&gt; + Unpin + &#39;static,
/// B: TryFuture&lt;Error = E&gt; + Unpin + &#39;static,
/// E: &#39;static,
/// {
/// future::try_select(a, b).then(|res| -&gt; Box&lt;dyn Future&lt;Output = Result&lt;_, _&gt;&gt; + Unpin&gt; {
/// match res {
/// Ok(Either::Left((x, b))) =&gt; Box::new(b.map_ok(move |y| (x, y))),
/// Ok(Either::Right((y, a))) =&gt; Box::new(a.map_ok(move |x| (x, y))),
/// Err(Either::Left((e, _))) =&gt; Box::new(future::err(e)),
/// Err(Either::Right((e, _))) =&gt; Box::new(future::err(e)),
/// }
/// })
/// }
/// ```
</span><span class="kw">pub fn </span>try_select&lt;A, B&gt;(future1: A, future2: B) -&gt; TrySelect&lt;A, B&gt;
<span class="kw">where
</span>A: TryFuture + Unpin,
B: TryFuture + Unpin,
{
<span class="kw">super</span>::assert_future::&lt;<span class="prelude-ty">Result</span>&lt;EitherOk&lt;A, B&gt;, EitherErr&lt;A, B&gt;&gt;, <span class="kw">_</span>&gt;(TrySelect {
inner: <span class="prelude-val">Some</span>((future1, future2)),
})
}
<span class="kw">impl</span>&lt;A: Unpin, B: Unpin&gt; Future <span class="kw">for </span>TrySelect&lt;A, B&gt;
<span class="kw">where
</span>A: TryFuture,
B: TryFuture,
{
<span class="kw">type </span>Output = <span class="prelude-ty">Result</span>&lt;EitherOk&lt;A, B&gt;, EitherErr&lt;A, B&gt;&gt;;
<span class="kw">fn </span>poll(<span class="kw-2">mut </span><span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;<span class="self">Self</span>::Output&gt; {
<span class="kw">let </span>(<span class="kw-2">mut </span>a, <span class="kw-2">mut </span>b) = <span class="self">self</span>.inner.take().expect(<span class="string">&quot;cannot poll Select twice&quot;</span>);
<span class="kw">match </span>a.try_poll_unpin(cx) {
Poll::Ready(<span class="prelude-val">Err</span>(x)) =&gt; Poll::Ready(<span class="prelude-val">Err</span>(Either::Left((x, b)))),
Poll::Ready(<span class="prelude-val">Ok</span>(x)) =&gt; Poll::Ready(<span class="prelude-val">Ok</span>(Either::Left((x, b)))),
Poll::Pending =&gt; <span class="kw">match </span>b.try_poll_unpin(cx) {
Poll::Ready(<span class="prelude-val">Err</span>(x)) =&gt; Poll::Ready(<span class="prelude-val">Err</span>(Either::Right((x, a)))),
Poll::Ready(<span class="prelude-val">Ok</span>(x)) =&gt; Poll::Ready(<span class="prelude-val">Ok</span>(Either::Right((x, a)))),
Poll::Pending =&gt; {
<span class="self">self</span>.inner = <span class="prelude-val">Some</span>((a, b));
Poll::Pending
}
},
}
}
}
</code></pre></div>
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