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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="API documentation for the Rust `repeat_with` fn in crate `nom`."><meta name="keywords" content="rust, rustlang, rust-lang, repeat_with"><title>nom::lib::std::iter::repeat_with - 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="../../../../light.css" id="themeStyle"><script src="../../../../storage.js"></script><noscript><link rel="stylesheet" href="../../../../noscript.css"></noscript><link rel="shortcut icon" href="../../../../favicon.ico"><style type="text/css">#crate-search{background-image:url("../../../../down-arrow.svg");}</style></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">☰</div><a href='../../../../nom/index.html'><div class='logo-container'><img src='../../../../rust-logo.png' alt='logo'></div></a><div class="sidebar-elems"><p class='location'><a href='../../../index.html'>nom</a>::<wbr><a href='../../index.html'>lib</a>::<wbr><a href='../index.html'>std</a>::<wbr><a href='index.html'>iter</a></p><script>window.sidebarCurrent = {name: 'repeat_with', ty: 'fn', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></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"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" disabled autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../../../../settings.html"><img src="../../../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span class='since' title='Stable since Rust version 1.28.0'>1.28.0</span><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='https://doc.rust-lang.org/nightly/src/core/iter/sources.rs.html#199-201' title='goto source code'>[src]</a></span><span class='in-band'>Function <a href='../../../index.html'>nom</a>::<wbr><a href='../../index.html'>lib</a>::<wbr><a href='../index.html'>std</a>::<wbr><a href='index.html'>iter</a>::<wbr><a class="fn" href=''>repeat_with</a></span></h1><pre class='rust fn'>pub fn repeat_with<A, F>(repeater: F) -> <a class="struct" href="../../../../nom/lib/std/iter/struct.RepeatWith.html" title="struct nom::lib::std::iter::RepeatWith">RepeatWith</a><F> <span class="where fmt-newline">where<br> F: <a class="trait" href="../../../../nom/lib/std/prelude/v1/v1/trait.FnMut.html" title="trait nom::lib::std::prelude::v1::v1::FnMut">FnMut</a>() -> A, </span></pre><div class='docblock'><p>Creates a new iterator that repeats elements of type <code>A</code> endlessly by
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applying the provided closure, the repeater, <code>F: FnMut() -> A</code>.</p>
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<p>The <code>repeat_with()</code> function calls the repeater over and over again.</p>
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<p>Infinite iterators like <code>repeat_with()</code> are often used with adapters like
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<a href="trait.Iterator.html#method.take"><code>take</code></a>, in order to make them finite.</p>
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<p>If the element type of the iterator you need implements <code>Clone</code>, and
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it is OK to keep the source element in memory, you should instead use
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the <a href="fn.repeat.html"><code>repeat</code></a> function.</p>
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<p>An iterator produced by <code>repeat_with()</code> is not a <code>DoubleEndedIterator</code>.
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If you need <code>repeat_with()</code> to return a <code>DoubleEndedIterator</code>,
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please open a GitHub issue explaining your use case.</p>
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<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
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<p>Basic usage:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">iter</span>;
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<span class="comment">// let's assume we have some value of a type that is not `Clone`</span>
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<span class="comment">// or which don't want to have in memory just yet because it is expensive:</span>
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<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">PartialEq</span>, <span class="ident">Debug</span>)]</span>
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<span class="kw">struct</span> <span class="ident">Expensive</span>;
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<span class="comment">// a particular value forever:</span>
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">things</span> <span class="op">=</span> <span class="ident">iter</span>::<span class="ident">repeat_with</span>(<span class="op">|</span><span class="op">|</span> <span class="ident">Expensive</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="prelude-val">Some</span>(<span class="ident">Expensive</span>), <span class="ident">things</span>.<span class="ident">next</span>());
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="prelude-val">Some</span>(<span class="ident">Expensive</span>), <span class="ident">things</span>.<span class="ident">next</span>());
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="prelude-val">Some</span>(<span class="ident">Expensive</span>), <span class="ident">things</span>.<span class="ident">next</span>());
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="prelude-val">Some</span>(<span class="ident">Expensive</span>), <span class="ident">things</span>.<span class="ident">next</span>());
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="prelude-val">Some</span>(<span class="ident">Expensive</span>), <span class="ident">things</span>.<span class="ident">next</span>());</pre></div>
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<p>Using mutation and going finite:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">iter</span>;
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<span class="comment">// From the zeroth to the third power of two:</span>
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">curr</span> <span class="op">=</span> <span class="number">1</span>;
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">pow2</span> <span class="op">=</span> <span class="ident">iter</span>::<span class="ident">repeat_with</span>(<span class="op">|</span><span class="op">|</span> { <span class="kw">let</span> <span class="ident">tmp</span> <span class="op">=</span> <span class="ident">curr</span>; <span class="ident">curr</span> <span class="kw-2">*</span><span class="op">=</span> <span class="number">2</span>; <span class="ident">tmp</span> })
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.<span class="ident">take</span>(<span class="number">4</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="prelude-val">Some</span>(<span class="number">1</span>), <span class="ident">pow2</span>.<span class="ident">next</span>());
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="prelude-val">Some</span>(<span class="number">2</span>), <span class="ident">pow2</span>.<span class="ident">next</span>());
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="prelude-val">Some</span>(<span class="number">4</span>), <span class="ident">pow2</span>.<span class="ident">next</span>());
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="prelude-val">Some</span>(<span class="number">8</span>), <span class="ident">pow2</span>.<span class="ident">next</span>());
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<span class="comment">// ... and now we're done</span>
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="prelude-val">None</span>, <span class="ident">pow2</span>.<span class="ident">next</span>());</pre></div>
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