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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 = "Apply a `Parser`, producing `None` on `ErrMode::Backtrack`." > < title > opt in winnow::combinator - Rust< / title > < script > if ( window . location . protocol !== "file:" ) document . write ( ` <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"> ` ) < / script > < link rel = "stylesheet" href = "../../static.files/normalize-76eba96aa4d2e634.css" > < link rel = "stylesheet" href = "../../static.files/rustdoc-e935ef01ae1c1829.css" > < meta name = "rustdoc-vars" data-root-path = "../../" data-static-root-path = "../../static.files/" data-current-crate = "winnow" data-themes = "" data-resource-suffix = "" data-rustdoc-version = "1.78.0 (9b00956e5 2024-04-29)" data-channel = "1.78.0" data-search-js = "search-42d8da7a6b9792c2.js" data-settings-js = "settings-4313503d2e1961c2.js" > < script src = "../../static.files/storage-4c98445ec4002617.js" > < / script > < script defer src = "sidebar-items.js" > < / script > < script defer src = "../../static.files/main-12cf3b4f4f9dc36d.js" > < / script > < noscript > < link rel = "stylesheet" href = "../../static.files/noscript-04d5337699b92874.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" title = "show sidebar" > < / button > < / nav > < nav class = "sidebar" > < div class = "sidebar-crate" > < h2 > < a href = "../../winnow/index.html" > winnow< / a > < span class = "version" > 0.6.7< / span > < / h2 > < / div > < div class = "sidebar-elems" > < h2 > < a href = "index.html" > In winnow::combinator< / 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 = "../../winnow/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 ‘ ’ ‘ ’ 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" > winnow< / a > ::< wbr > < a href = "index.html" > combinator< / a > ::< wbr > < a class = "fn" href = "#" > opt< / 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/winnow/combinator/core.rs.html#97-115" > source< / a > · < button id = "toggle-all-docs" title = "collapse all docs" > [< span > − < / span > ]< / button > < / span > < / div > < pre class = "rust item-decl" > < code > pub fn opt< Input: < a class = "trait" href = "../stream/trait.Stream.html" title = "trait winnow::stream::Stream" > Stream< / a > , Output, Error, ParseNext> (
parser: ParseNext
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) -> impl < a class = "trait" href = "../trait.Parser.html" title = "trait winnow::Parser" > Parser< / a > < Input, < a class = "enum" href = "https://doc.rust-lang.org/1.78.0/core/option/enum.Option.html" title = "enum core::option::Option" > Option< / a > < Output> , Error> < div class = "where" > where
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ParseNext: < a class = "trait" href = "../trait.Parser.html" title = "trait winnow::Parser" > Parser< / a > < Input, Output, Error> ,
Error: < a class = "trait" href = "../error/trait.ParserError.html" title = "trait winnow::error::ParserError" > ParserError< / a > < Input> ,< / div > < / code > < / pre > < details class = "toggle top-doc" open > < summary class = "hideme" > < span > Expand description< / span > < / summary > < div class = "docblock" > < p > Apply a < a href = "../trait.Parser.html" title = "trait winnow::Parser" > < code > Parser< / code > < / a > , producing < code > None< / code > on < a href = "../error/enum.ErrMode.html#variant.Backtrack" title = "variant winnow::error::ErrMode::Backtrack" > < code > ErrMode::Backtrack< / code > < / a > .< / p >
< p > To chain an error up, see < a href = "fn.cut_err.html" title = "fn winnow::combinator::cut_err" > < code > cut_err< / code > < / a > .< / p >
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< h2 id = "example" > < a class = "doc-anchor" href = "#example" > §< / a > Example< / h2 >
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< div class = "example-wrap" > < pre class = "rust rust-example-rendered" > < code > < span class = "kw" > use < / span > winnow::combinator::opt;
< span class = "kw" > use < / span > winnow::ascii::alpha1;
< span class = "kw" > fn < / span > parser(i: < span class = "kw-2" > & < / span > str) -> IResult< < span class = "kw-2" > & < / span > str, < span class = "prelude-ty" > Option< / span > < < span class = "kw-2" > & < / span > str> > {
opt(alpha1).parse_peek(i)
}
< span class = "macro" > assert_eq!< / span > (parser(< span class = "string" > "abcd;"< / span > ), < span class = "prelude-val" > Ok< / span > ((< span class = "string" > ";"< / span > , < span class = "prelude-val" > Some< / span > (< span class = "string" > "abcd"< / span > ))));
< span class = "macro" > assert_eq!< / span > (parser(< span class = "string" > "123;"< / span > ), < span class = "prelude-val" > Ok< / span > ((< span class = "string" > "123;"< / span > , < span class = "prelude-val" > None< / span > )));< / code > < / pre > < / div >
< / div > < / details > < / section > < / div > < / main > < / body > < / html >
