| <!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."><meta name="keywords" content="rust, rustlang, rust-lang, select_with_strategy"><title>select_with_strategy in futures::prelude::stream - 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 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="sidebar-items.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 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><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::stream</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">stream</a>::<wbr><a class="fn" href="#">select_with_strategy</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/stream/select_with_strategy.rs.html#139-148">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 select_with_strategy<St1, St2, Clos, State>(<br> stream1: St1,<br> stream2: St2,<br> which: Clos<br>) -> <a class="struct" href="../../stream/struct.SelectWithStrategy.html" title="struct futures::stream::SelectWithStrategy">SelectWithStrategy</a><St1, St2, Clos, State><span class="where fmt-newline">where<br> St1: <a class="trait" href="../../stream/trait.Stream.html" title="trait futures::stream::Stream">Stream</a>,<br> 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>>,<br> Clos: <a class="trait" href="https://doc.rust-lang.org/nightly/core/ops/function/trait.FnMut.html" title="trait core::ops::function::FnMut">FnMut</a>(<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>State) -> <a class="enum" href="../../stream/enum.PollNext.html" title="enum futures::stream::PollNext">PollNext</a>,<br> State: <a class="trait" href="https://doc.rust-lang.org/nightly/core/default/trait.Default.html" title="trait core::default::Default">Default</a>,</span></code></pre></div><details class="rustdoc-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 |
| closure to tell <a href="../../stream/struct.SelectWithStrategy.html" title="SelectWithStrategy"><code>SelectWithStrategy</code></a> which stream to poll. The closure can |
| store state on <code>SelectWithStrategy</code> to which it will receive a <code>&mut</code> on every |
| invocation. This allows basing the strategy on prior choices.</p> |
| <p>After one of the two input streams completes, the remaining one will be |
| polled exclusively. The returned stream completes when both input |
| streams have completed.</p> |
| <p>Note that this function consumes both streams and returns a wrapped |
| version of them.</p> |
| <h3 id="examples"><a href="#examples">Examples</a></h3><h4 id="priority"><a href="#priority">Priority</a></h4> |
| <p>This example shows how to always prioritize the left stream.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>futures::stream::{ repeat, select_with_strategy, PollNext, StreamExt }; |
| |
| <span class="kw">let </span>left = repeat(<span class="number">1</span>); |
| <span class="kw">let </span>right = repeat(<span class="number">2</span>); |
| |
| <span class="comment">// We don't need any state, so let's make it an empty tuple. |
| // We must provide some type here, as there is no way for the compiler |
| // to infer it. As we don't need to capture variables, we can just |
| // use a function pointer instead of a closure. |
| </span><span class="kw">fn </span>prio_left(<span class="kw">_</span>: <span class="kw-2">&mut </span>()) -> PollNext { PollNext::Left } |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>out = select_with_strategy(left, right, prio_left); |
| |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">100 </span>{ |
| <span class="comment">// Whenever we poll out, we will alwas get `1`. |
| </span><span class="macro">assert_eq!</span>(<span class="number">1</span>, out.select_next_some().<span class="kw">await</span>); |
| }</code></pre></div> |
| <h4 id="round-robin"><a href="#round-robin">Round Robin</a></h4> |
| <p>This example shows how to select from both streams round robin. |
| Note: this special case is provided by [<code>futures-util::stream::select</code>].</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>futures::stream::{ repeat, select_with_strategy, PollNext, StreamExt }; |
| |
| <span class="kw">let </span>left = repeat(<span class="number">1</span>); |
| <span class="kw">let </span>right = repeat(<span class="number">2</span>); |
| |
| <span class="kw">let </span>rrobin = |last: <span class="kw-2">&mut </span>PollNext| last.toggle(); |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>out = select_with_strategy(left, right, rrobin); |
| |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">100 </span>{ |
| <span class="comment">// We should be alternating now. |
| </span><span class="macro">assert_eq!</span>(<span class="number">1</span>, out.select_next_some().<span class="kw">await</span>); |
| <span class="macro">assert_eq!</span>(<span class="number">2</span>, out.select_next_some().<span class="kw">await</span>); |
| }</code></pre></div> |
| </div></details></section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="futures" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
