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67 lines
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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 `switch` macro in crate `nom`."><meta name="keywords" content="rust, rustlang, rust-lang, switch"><title>nom::switch - 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 macro"><!--[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></p><script>window.sidebarCurrent = {name: 'switch', ty: 'macro', 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 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='../src/nom/branch.rs.html#439-488' title='goto source code'>[src]</a></span><span class='in-band'>Macro <a href='index.html'>nom</a>::<wbr><a class="macro" href=''>switch</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><div class="example-wrap"><pre class="rust macro">
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<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">switch</span> {
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(<span class="ident">__impl</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">submac</span>:<span class="macro">ident</span><span class="macro">!</span>( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">args</span>:<span class="ident">tt</span>)<span class="op">*</span> ), $( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span>)<span class="op">|</span><span class="op">+</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">subrule</span>:<span class="macro">ident</span><span class="macro">!</span>( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">args2</span>:<span class="ident">tt</span>)<span class="op">*</span> ))<span class="op">|</span><span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">submac</span>:<span class="macro">ident</span><span class="macro">!</span>( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">args</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>), $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">rest</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=</span><span class="op">></span> { ... };
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>:<span class="ident">path</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">rest</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=</span><span class="op">></span> { ... };
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}</pre></div>
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</div><div class='docblock'><p><code>switch!(I -> IResult<I,P>, P => I -> IResult<I,O> | ... | P => I -> IResult<I,O> ) => I -> IResult<I, O></code>
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choose the next parser depending on the result of the first one, if successful,
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and returns the result of the second parser</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="macro">named</span><span class="macro">!</span>(<span class="ident">sw</span>,
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<span class="macro">switch</span><span class="macro">!</span>(<span class="macro">take</span><span class="macro">!</span>(<span class="number">4</span>),
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<span class="string">b"abcd"</span> <span class="op">=</span><span class="op">></span> <span class="macro">tag</span><span class="macro">!</span>(<span class="string">"XYZ"</span>) <span class="op">|</span>
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<span class="string">b"efgh"</span> <span class="op">=</span><span class="op">></span> <span class="macro">tag</span><span class="macro">!</span>(<span class="string">"123"</span>)
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)
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);
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<span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> <span class="string">b"abcdXYZ123"</span>;
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<span class="kw">let</span> <span class="ident">b</span> <span class="op">=</span> <span class="string">b"abcdef"</span>;
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<span class="kw">let</span> <span class="ident">c</span> <span class="op">=</span> <span class="string">b"efgh123"</span>;
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<span class="kw">let</span> <span class="ident">d</span> <span class="op">=</span> <span class="string">b"blah"</span>;
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">sw</span>(<span class="kw-2">&</span><span class="ident">a</span>[..]), <span class="prelude-val">Ok</span>((<span class="kw-2">&</span><span class="string">b"123"</span>[..], <span class="kw-2">&</span><span class="string">b"XYZ"</span>[..])));
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">sw</span>(<span class="kw-2">&</span><span class="ident">b</span>[..]), <span class="prelude-val">Err</span>(<span class="prelude-val">Err</span>::<span class="ident">Error</span>(<span class="macro">error_node_position</span><span class="macro">!</span>(<span class="kw-2">&</span><span class="string">b"abcdef"</span>[..], <span class="ident">ErrorKind</span>::<span class="ident">Switch</span>,
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<span class="macro">error_position</span><span class="macro">!</span>(<span class="kw-2">&</span><span class="string">b"ef"</span>[..], <span class="ident">ErrorKind</span>::<span class="ident">Tag</span>)))));
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">sw</span>(<span class="kw-2">&</span><span class="ident">c</span>[..]), <span class="prelude-val">Ok</span>((<span class="kw-2">&</span><span class="string">b""</span>[..], <span class="kw-2">&</span><span class="string">b"123"</span>[..])));
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">sw</span>(<span class="kw-2">&</span><span class="ident">d</span>[..]), <span class="prelude-val">Err</span>(<span class="prelude-val">Err</span>::<span class="ident">Error</span>(<span class="macro">error_position</span><span class="macro">!</span>(<span class="kw-2">&</span><span class="string">b"blah"</span>[..], <span class="ident">ErrorKind</span>::<span class="ident">Switch</span>))));</pre></div>
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<p>You can specify a default case like with a normal match, using <code>_</code></p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="macro">named</span><span class="macro">!</span>(<span class="ident">sw</span>,
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<span class="macro">switch</span><span class="macro">!</span>(<span class="macro">take</span><span class="macro">!</span>(<span class="number">4</span>),
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<span class="string">b"abcd"</span> <span class="op">=</span><span class="op">></span> <span class="macro">tag</span><span class="macro">!</span>(<span class="string">"XYZ"</span>) <span class="op">|</span>
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<span class="kw">_</span> <span class="op">=</span><span class="op">></span> <span class="macro">value</span><span class="macro">!</span>(<span class="kw-2">&</span><span class="string">b"default"</span>[..])
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)
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);
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<span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> <span class="string">b"abcdXYZ123"</span>;
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<span class="kw">let</span> <span class="ident">b</span> <span class="op">=</span> <span class="string">b"blah"</span>;
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">sw</span>(<span class="kw-2">&</span><span class="ident">a</span>[..]), <span class="prelude-val">Ok</span>((<span class="kw-2">&</span><span class="string">b"123"</span>[..], <span class="kw-2">&</span><span class="string">b"XYZ"</span>[..])));
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">sw</span>(<span class="kw-2">&</span><span class="ident">b</span>[..]), <span class="prelude-val">Ok</span>((<span class="kw-2">&</span><span class="string">b""</span>[..], <span class="kw-2">&</span><span class="string">b"default"</span>[..])));</pre></div>
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<p>Due to limitations in Rust macros, it is not possible to have simple functions on the right hand
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side of pattern, like this:</p>
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<div class='information'><div class='tooltip ignore'>ⓘ<span class='tooltiptext'>This example is not tested</span></div></div><div class="example-wrap"><pre class="rust rust-example-rendered ignore">
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<span class="macro">named</span><span class="macro">!</span>(<span class="ident">xyz</span>, <span class="macro">tag</span><span class="macro">!</span>(<span class="string">"XYZ"</span>));
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<span class="macro">named</span><span class="macro">!</span>(<span class="ident">num</span>, <span class="macro">tag</span><span class="macro">!</span>(<span class="string">"123"</span>));
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<span class="macro">named</span><span class="macro">!</span>(<span class="ident">sw</span>,
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<span class="macro">switch</span><span class="macro">!</span>(<span class="macro">take</span><span class="macro">!</span>(<span class="number">4</span>),
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<span class="string">b"abcd"</span> <span class="op">=</span><span class="op">></span> <span class="ident">xyz</span> <span class="op">|</span>
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<span class="string">b"efgh"</span> <span class="op">=</span><span class="op">></span> <span class="number">123</span>
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)
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);</pre></div>
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<p>If you want to pass your own functions instead, you can use the <code>call!</code> combinator as follows:</p>
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<div class='information'><div class='tooltip ignore'>ⓘ<span class='tooltiptext'>This example is not tested</span></div></div><div class="example-wrap"><pre class="rust rust-example-rendered ignore">
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<span class="macro">named</span><span class="macro">!</span>(<span class="ident">xyz</span>, <span class="macro">tag</span><span class="macro">!</span>(<span class="string">"XYZ"</span>));
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<span class="macro">named</span><span class="macro">!</span>(<span class="ident">num</span>, <span class="macro">tag</span><span class="macro">!</span>(<span class="string">"123"</span>));
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<span class="macro">named</span><span class="macro">!</span>(<span class="ident">sw</span>,
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<span class="macro">switch</span><span class="macro">!</span>(<span class="macro">take</span><span class="macro">!</span>(<span class="number">4</span>),
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<span class="string">b"abcd"</span> <span class="op">=</span><span class="op">></span> <span class="macro">call</span><span class="macro">!</span>(<span class="ident">xyz</span>) <span class="op">|</span>
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<span class="string">b"efgh"</span> <span class="op">=</span><span class="op">></span> <span class="macro">call</span><span class="macro">!</span>(<span class="ident">num</span>)
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)
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);</pre></div>
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