| <!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="Parses `parser` and outputs `Some(value)` if it succeeds, `None` if it fails without consuming any input. Fails if `parser` fails after having committed some input."><meta name="keywords" content="rust, rustlang, rust-lang, optional"><title>optional in combine - 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="../combine/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="../combine/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 combine</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">combine</a>::<wbr><a class="fn" href="#">optional</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/combine/parser/choice.rs.html#683-689">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 optional<Input, P>(parser: P) -> <a class="struct" href="parser/choice/struct.Optional.html" title="struct combine::parser::choice::Optional">Optional</a><P><span class="where fmt-newline">where<br> Input: <a class="trait" href="trait.Stream.html" title="trait combine::Stream">Stream</a>,<br> P: <a class="trait" href="trait.Parser.html" title="trait combine::Parser">Parser</a><Input>,</span></code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Parses <code>parser</code> and outputs <code>Some(value)</code> if it succeeds, <code>None</code> if it fails without |
| consuming any input. Fails if <code>parser</code> fails after having committed some input.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let </span><span class="kw-2">mut </span>parser = optional(string(<span class="string">"hello"</span>)); |
| <span class="macro">assert_eq!</span>(parser.parse(<span class="string">"hello"</span>), <span class="prelude-val">Ok</span>((<span class="prelude-val">Some</span>(<span class="string">"hello"</span>), <span class="string">""</span>))); |
| <span class="macro">assert_eq!</span>(parser.parse(<span class="string">"world"</span>), <span class="prelude-val">Ok</span>((<span class="prelude-val">None</span>, <span class="string">"world"</span>))); |
| <span class="macro">assert!</span>(parser.parse(<span class="string">"heya"</span>).is_err());</code></pre></div> |
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