mentat/tokio/prelude/stream/fn.unfold.html
2018-08-22 17:04:13 +00:00

162 lines
No EOL
9.3 KiB
HTML
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

<!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="API documentation for the Rust `unfold` fn in crate `tokio`.">
<meta name="keywords" content="rust, rustlang, rust-lang, unfold">
<title>tokio::prelude::stream::unfold - Rust</title>
<link rel="stylesheet" type="text/css" href="../../../normalize.css">
<link rel="stylesheet" type="text/css" href="../../../rustdoc.css" id="mainThemeStyle">
<link rel="stylesheet" type="text/css" href="../../../dark.css">
<link rel="stylesheet" type="text/css" href="../../../main.css" id="themeStyle">
<script src="../../../storage.js"></script>
</head>
<body class="rustdoc fn">
<!--[if lte IE 8]>
<div class="warning">
This old browser is unsupported and will most likely display funky
things.
</div>
<![endif]-->
<nav class="sidebar">
<div class="sidebar-menu">&#9776;</div>
<p class='location'><a href='../../index.html'>tokio</a>::<wbr><a href='../index.html'>prelude</a>::<wbr><a href='index.html'>stream</a></p><script>window.sidebarCurrent = {name: 'unfold', ty: 'fn', relpath: ''};</script><script defer src="sidebar-items.js"></script>
</nav>
<div class="theme-picker">
<button id="theme-picker" aria-label="Pick another theme!">
<img src="../../../brush.svg" width="18" alt="Pick another theme!">
</button>
<div id="theme-choices"></div>
</div>
<script src="../../../theme.js"></script>
<nav class="sub">
<form class="search-form js-only">
<div class="search-container">
<input class="search-input" name="search"
autocomplete="off"
placeholder="Click or press S to search, ? for more options…"
type="search">
</div>
</form>
</nav>
<section id='main' class="content">
<h1 class='fqn'><span class='in-band'>Function <a href='../../index.html'>tokio</a>::<wbr><a href='../index.html'>prelude</a>::<wbr><a href='index.html'>stream</a>::<wbr><a class="fn" href=''>unfold</a></span><span class='out-of-band'><span id='render-detail'>
<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
[<span class='inner'>&#x2212;</span>]
</a>
</span><a class='srclink' href='../../../src/futures/stream/unfold.rs.html#49-57' title='goto source code'>[src]</a></span></h1>
<pre class='rust fn'>pub fn unfold&lt;T, F, Fut, It&gt;(init: T, f: F) -&gt; <a class="struct" href="../../../tokio/prelude/stream/struct.Unfold.html" title="struct tokio::prelude::stream::Unfold">Unfold</a>&lt;T, F, Fut&gt; <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;F: <a class="trait" href="https://doc.rust-lang.org/nightly/core/ops/function/trait.FnMut.html" title="trait core::ops::function::FnMut">FnMut</a>(T) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a>&lt;Fut&gt;,<br>&nbsp;&nbsp;&nbsp;&nbsp;Fut: <a class="trait" href="../../../tokio/prelude/trait.IntoFuture.html" title="trait tokio::prelude::IntoFuture">IntoFuture</a>&lt;Item = <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.tuple.html">(</a>It, T<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.tuple.html">)</a>&gt;,&nbsp;</span></pre><div class='docblock'><p>Creates a <code>Stream</code> from a seed and a closure returning a <code>Future</code>.</p>
<p>This function is the dual for the <code>Stream::fold()</code> adapter: while
<code>Stream::fold()</code> reduces a <code>Stream</code> to one single value, <code>unfold()</code> creates a
<code>Stream</code> from a seed value.</p>
<p><code>unfold()</code> will call the provided closure with the provided seed, then wait
for the returned <code>Future</code> to complete with <code>(a, b)</code>. It will then yield the
value <code>a</code>, and use <code>b</code> as the next internal state.</p>
<p>If the closure returns <code>None</code> instead of <code>Some(Future)</code>, then the <code>unfold()</code>
will stop producing items and return <code>Ok(Async::Ready(None))</code> in future
calls to <code>poll()</code>.</p>
<p>In case of error generated by the returned <code>Future</code>, the error will be
returned by the <code>Stream</code>. The <code>Stream</code> will then yield
<code>Ok(Async::Ready(None))</code> in future calls to <code>poll()</code>.</p>
<p>This function can typically be used when wanting to go from the &quot;world of
futures&quot; to the &quot;world of streams&quot;: the provided closure can build a
<code>Future</code> using other library functions working on futures, and <code>unfold()</code>
will turn it into a <code>Stream</code> by repeating the operation.</p>
<h1 id="example" class="section-header"><a href="#example">Example</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">futures</span>::<span class="ident">stream</span>::{<span class="self">self</span>, <span class="ident">Stream</span>};
<span class="kw">use</span> <span class="ident">futures</span>::<span class="ident">future</span>::{<span class="self">self</span>, <span class="ident">Future</span>};
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">stream</span> <span class="op">=</span> <span class="ident">stream</span>::<span class="ident">unfold</span>(<span class="number">0</span>, <span class="op">|</span><span class="ident">state</span><span class="op">|</span> {
<span class="kw">if</span> <span class="ident">state</span> <span class="op">&lt;=</span> <span class="number">2</span> {
<span class="kw">let</span> <span class="ident">next_state</span> <span class="op">=</span> <span class="ident">state</span> <span class="op">+</span> <span class="number">1</span>;
<span class="kw">let</span> <span class="ident">yielded</span> <span class="op">=</span> <span class="ident">state</span> <span class="op">*</span> <span class="number">2</span>;
<span class="kw">let</span> <span class="ident">fut</span> <span class="op">=</span> <span class="ident">future</span>::<span class="ident">ok</span>::<span class="op">&lt;</span>_, <span class="ident">u32</span><span class="op">&gt;</span>((<span class="ident">yielded</span>, <span class="ident">next_state</span>));
<span class="prelude-val">Some</span>(<span class="ident">fut</span>)
} <span class="kw">else</span> {
<span class="prelude-val">None</span>
}
});
<span class="kw">let</span> <span class="ident">result</span> <span class="op">=</span> <span class="ident">stream</span>.<span class="ident">collect</span>().<span class="ident">wait</span>();
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">result</span>, <span class="prelude-val">Ok</span>(<span class="macro">vec</span><span class="macro">!</span>[<span class="number">0</span>, <span class="number">2</span>, <span class="number">4</span>]));</pre>
</div></section>
<section id='search' class="content hidden"></section>
<section class="footer"></section>
<aside id="help" class="hidden">
<div>
<h1 class="hidden">Help</h1>
<div class="shortcuts">
<h2>Keyboard Shortcuts</h2>
<dl>
<dt><kbd>?</kbd></dt>
<dd>Show this help dialog</dd>
<dt><kbd>S</kbd></dt>
<dd>Focus the search field</dd>
<dt><kbd></kbd></dt>
<dd>Move up in search results</dd>
<dt><kbd></kbd></dt>
<dd>Move down in search results</dd>
<dt><kbd></kbd></dt>
<dd>Switch tab</dd>
<dt><kbd>&#9166;</kbd></dt>
<dd>Go to active search result</dd>
<dt><kbd>+</kbd></dt>
<dd>Expand all sections</dd>
<dt><kbd>-</kbd></dt>
<dd>Collapse all sections</dd>
</dl>
</div>
<div class="infos">
<h2>Search Tricks</h2>
<p>
Prefix searches with a type followed by a colon (e.g.
<code>fn:</code>) to restrict the search to a given type.
</p>
<p>
Accepted types are: <code>fn</code>, <code>mod</code>,
<code>struct</code>, <code>enum</code>,
<code>trait</code>, <code>type</code>, <code>macro</code>,
and <code>const</code>.
</p>
<p>
Search functions by type signature (e.g.
<code>vec -> usize</code> or <code>* -> vec</code>)
</p>
</div>
</div>
</aside>
<script>
window.rootPath = "../../../";
window.currentCrate = "tokio";
</script>
<script src="../../../main.js"></script>
<script defer src="../../../search-index.js"></script>
</body>
</html>