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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="This function will attempt to pull items from both streams. You provide a closure to tell `SelectWithStrategy` which stream to poll. The closure can store state on `SelectWithStrategy` to which it will receive a `&mut` on every invocation. This allows basing the strategy on prior choices."><title>select_with_strategy in futures::prelude::stream - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><link rel="stylesheet" href="../../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../../static.files/rustdoc-ac92e1bbe349e143.css"><meta name="rustdoc-vars" data-root-path="../../../" data-static-root-path="../../../static.files/" data-current-crate="futures" data-themes="" data-resource-suffix="" data-rustdoc-version="1.76.0 (07dca489a 2024-02-04)" data-channel="1.76.0" data-search-js="search-2b6ce74ff89ae146.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../../static.files/storage-f2adc0d6ca4d09fb.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../../static.files/main-305769736d49e732.js"></script><noscript><link rel="stylesheet" href="../../../static.files/noscript-feafe1bb7466e4bd.css"></noscript><link rel="alternate icon" type="image/png" href="../../../static.files/favicon-16x16-8b506e7a72182f1c.png"><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">☰</button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../../futures/index.html">futures</a><span class="version">0.3.28</span></h2></div><div class="sidebar-elems"><h2><a href="index.html">In futures::prelude::stream</a></h2></div></nav><div class="sidebar-resizer"></div>
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<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../../../futures/all.html" title="show sidebar"></a></div><input class="search-input" name="search" aria-label="Run search in the documentation" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" tabindex="-1"><a href="../../../help.html" title="help">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1>Function <a href="../../index.html">futures</a>::<wbr><a href="../index.html">prelude</a>::<wbr><a href="index.html">stream</a>::<wbr><a class="fn" href="#">select_with_strategy</a><button id="copy-path" title="Copy item path to clipboard"><img src="../../../static.files/clipboard-7571035ce49a181d.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="src" href="../../../src/futures_util/stream/select_with_strategy.rs.html#139-148">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><pre class="rust item-decl"><code>pub fn select_with_strategy<St1, St2, Clos, State>(
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stream1: St1,
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stream2: St2,
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which: Clos
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) -> <a class="struct" href="../../stream/struct.SelectWithStrategy.html" title="struct futures::stream::SelectWithStrategy">SelectWithStrategy</a><St1, St2, Clos, State><div class="where">where
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St1: <a class="trait" href="../../stream/trait.Stream.html" title="trait futures::stream::Stream">Stream</a>,
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St2: <a class="trait" href="../../stream/trait.Stream.html" title="trait futures::stream::Stream">Stream</a><Item = <St1 as <a class="trait" href="../../stream/trait.Stream.html" title="trait futures::stream::Stream">Stream</a>>::<a class="associatedtype" href="../../stream/trait.Stream.html#associatedtype.Item" title="type futures::stream::Stream::Item">Item</a>>,
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Clos: <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/ops/function/trait.FnMut.html" title="trait core::ops::function::FnMut">FnMut</a>(<a class="primitive" href="https://doc.rust-lang.org/1.76.0/std/primitive.reference.html">&mut State</a>) -> <a class="enum" href="../../stream/enum.PollNext.html" title="enum futures::stream::PollNext">PollNext</a>,
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State: <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/default/trait.Default.html" title="trait core::default::Default">Default</a>,</div></code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>This function will attempt to pull items from both streams. You provide a
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closure to tell <a href="../../stream/struct.SelectWithStrategy.html" title="struct futures::stream::SelectWithStrategy"><code>SelectWithStrategy</code></a> which stream to poll. The closure can
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store state on <code>SelectWithStrategy</code> to which it will receive a <code>&mut</code> on every
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invocation. This allows basing the strategy on prior choices.</p>
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<p>After one of the two input streams completes, the remaining one will be
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polled exclusively. The returned stream completes when both input
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streams have completed.</p>
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<p>Note that this function consumes both streams and returns a wrapped
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version of them.</p>
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<h3 id="examples"><a href="#examples">Examples</a></h3><h4 id="priority"><a href="#priority">Priority</a></h4>
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<p>This example shows how to always prioritize the left stream.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>futures::stream::{ repeat, select_with_strategy, PollNext, StreamExt };
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<span class="kw">let </span>left = repeat(<span class="number">1</span>);
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<span class="kw">let </span>right = repeat(<span class="number">2</span>);
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<span class="comment">// We don't need any state, so let's make it an empty tuple.
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// We must provide some type here, as there is no way for the compiler
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// to infer it. As we don't need to capture variables, we can just
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// use a function pointer instead of a closure.
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</span><span class="kw">fn </span>prio_left(<span class="kw">_</span>: <span class="kw-2">&mut </span>()) -> PollNext { PollNext::Left }
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<span class="kw">let </span><span class="kw-2">mut </span>out = select_with_strategy(left, right, prio_left);
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<span class="kw">for _ in </span><span class="number">0</span>..<span class="number">100 </span>{
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<span class="comment">// Whenever we poll out, we will alwas get `1`.
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</span><span class="macro">assert_eq!</span>(<span class="number">1</span>, out.select_next_some().<span class="kw">await</span>);
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}</code></pre></div>
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<h4 id="round-robin"><a href="#round-robin">Round Robin</a></h4>
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<p>This example shows how to select from both streams round robin.
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Note: this special case is provided by [<code>futures-util::stream::select</code>].</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>futures::stream::{ repeat, select_with_strategy, PollNext, StreamExt };
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<span class="kw">let </span>left = repeat(<span class="number">1</span>);
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<span class="kw">let </span>right = repeat(<span class="number">2</span>);
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<span class="kw">let </span>rrobin = |last: <span class="kw-2">&mut </span>PollNext| last.toggle();
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<span class="kw">let </span><span class="kw-2">mut </span>out = select_with_strategy(left, right, rrobin);
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<span class="kw">for _ in </span><span class="number">0</span>..<span class="number">100 </span>{
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<span class="comment">// We should be alternating now.
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</span><span class="macro">assert_eq!</span>(<span class="number">1</span>, out.select_next_some().<span class="kw">await</span>);
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<span class="macro">assert_eq!</span>(<span class="number">2</span>, out.select_next_some().<span class="kw">await</span>);
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}</code></pre></div>
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</div></details></section></div></main></body></html> |