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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="Creates a future that is immediately ready with an Option of a value. Specifically this means that poll always returns Poll::Ready."><title>poll_immediate 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-b0742ba02757f159.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="1.83.0 (90b35a623 2024-11-26)" data-channel="1.83.0" data-search-js="search-f0d225181b97f9a4.js" data-settings-js="settings-805db61a62df4bd2.js" ><script src="../../static.files/storage-1d39b6787ed640ff.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../static.files/main-f070b9041d14864c.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-0111fcff984fae8f.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"><section id="rustdoc-toc"><h2 class="location"><a href="#">poll_<wbr>immediate</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#caution" title="Caution">Caution</a></li><li><a href="#examples" title="Examples">Examples</a><ul><li><a href="#reusing-a-future" title="Reusing a future">Reusing a future</a></li></ul></li></ul></section><div id="rustdoc-modnav"><h2><a href="index.html">In futures_<wbr>util::<wbr>future</a></h2></div></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"><span class="rustdoc-breadcrumbs"><a href="../index.html">futures_util</a>::<wbr><a href="index.html">future</a></span><h1>Function <span class="fn">poll_immediate</span><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><rustdoc-toolbar></rustdoc-toolbar><span class="sub-heading"><a class="src" href="../../src/futures_util/future/poll_immediate.rs.html#124-126">source</a> </span></div><pre class="rust item-decl"><code>pub fn poll_immediate&lt;F: <a class="trait" href="https://doc.rust-lang.org/1.83.0/core/future/future/trait.Future.html" title="trait core::future::future::Future">Future</a>&gt;(f: F) -&gt; <a class="struct" href="struct.PollImmediate.html" title="struct futures_util::future::PollImmediate">PollImmediate</a>&lt;F&gt; <a href="#" class="tooltip" data-notable-ty="PollImmediate&lt;F&gt;"></a></code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Creates a future that is immediately ready with an Option of a value.
Specifically this means that <a href="https://doc.rust-lang.org/1.83.0/core/future/future/trait.Future.html#tymethod.poll" title="method core::future::future::Future::poll">poll</a> always returns <a href="https://doc.rust-lang.org/1.83.0/core/task/poll/enum.Poll.html#variant.Ready" title="variant core::task::poll::Poll::Ready">Poll::Ready</a>.</p>
<h2 id="caution"><a class="doc-anchor" href="#caution">§</a>Caution</h2>
<p>When consuming the future by this function, note the following:</p>
<ul>
<li>This function does not guarantee that the future will run to completion, so it is generally incompatible with passing the non-cancellation-safe future by value.</li>
<li>Even if the future is cancellation-safe, creating and dropping new futures frequently may lead to performance problems.</li>
</ul>
<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="kw">let </span>r = future::poll_immediate(<span class="kw">async </span>{ <span class="number">1_u32 </span>});
<span class="macro">assert_eq!</span>(r.<span class="kw">await</span>, <span class="prelude-val">Some</span>(<span class="number">1</span>));
<span class="kw">let </span>p = future::poll_immediate(future::pending::&lt;i32&gt;());
<span class="macro">assert_eq!</span>(p.<span class="kw">await</span>, <span class="prelude-val">None</span>);</code></pre></div>
<h4 id="reusing-a-future"><a class="doc-anchor" href="#reusing-a-future">§</a>Reusing a future</h4>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>futures::{future, pin_mut};
<span class="kw">let </span>f = <span class="kw">async </span>{<span class="macro">futures::pending!</span>(); <span class="number">42_u8</span>};
<span class="macro">pin_mut!</span>(f);
<span class="macro">assert_eq!</span>(<span class="prelude-val">None</span>, future::poll_immediate(<span class="kw-2">&amp;mut </span>f).<span class="kw">await</span>);
<span class="macro">assert_eq!</span>(<span class="number">42</span>, f.<span class="kw">await</span>);</code></pre></div>
</div></details><script type="text/json" id="notable-traits-data">{"PollImmediate<F>":"<h3>Notable traits for <code><a class=\"struct\" href=\"struct.PollImmediate.html\" title=\"struct futures_util::future::PollImmediate\">PollImmediate</a>&lt;F&gt;</code></h3><pre><code><div class=\"where\">impl&lt;T, F&gt; <a class=\"trait\" href=\"https://doc.rust-lang.org/1.83.0/core/future/future/trait.Future.html\" title=\"trait core::future::future::Future\">Future</a> for <a class=\"struct\" href=\"struct.PollImmediate.html\" title=\"struct futures_util::future::PollImmediate\">PollImmediate</a>&lt;F&gt;<div class=\"where\">where\n F: <a class=\"trait\" href=\"https://doc.rust-lang.org/1.83.0/core/future/future/trait.Future.html\" title=\"trait core::future::future::Future\">Future</a>&lt;Output = T&gt;,</div></div><div class=\"where\"> type <a href=\"https://doc.rust-lang.org/1.83.0/core/future/future/trait.Future.html#associatedtype.Output\" class=\"associatedtype\">Output</a> = <a class=\"enum\" href=\"https://doc.rust-lang.org/1.83.0/core/option/enum.Option.html\" title=\"enum core::option::Option\">Option</a>&lt;T&gt;;</div>"}</script></section></div></main></body></html>