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85 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 `methods` mod in crate `nom`."><meta name="keywords" content="rust, rustlang, rust-lang, methods"><title>nom::methods - 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 mod"><!--[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><p class='location'>Module methods</p><div class="sidebar-elems"><p class='location'><a href='../index.html'>nom</a></p><script>window.sidebarCurrent = {name: 'methods', ty: 'mod', 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/methods.rs.html#1-627' title='goto source code'>[src]</a></span><span class='in-band'>Module <a href='../index.html'>nom</a>::<wbr><a class="mod" href=''>methods</a></span></h1><div class='docblock'><p>Method macro combinators</p>
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<p>These macros make parsers as methods of structs
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and that can take methods of structs to call
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as parsers.</p>
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<p>There is a trick to make them easier to assemble,
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combinators are defined 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">macro_rules</span><span class="macro">!</span> <span class="ident">tag</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">inp</span>: <span class="ident">expr</span>) <span class="op">=</span><span class="op">></span> (
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{
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...
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}
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);
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);</pre></div>
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<p>But when used as methods in other combinators, are used
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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">method</span><span class="macro">!</span>(<span class="ident">my_function</span><span class="op"><</span><span class="ident">Parser</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> <span class="op">></span>, <span class="self">self</span>, <span class="macro">tag</span><span class="macro">!</span>(<span class="string">"abcd"</span>));</pre></div>
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<p>Internally, other combinators will rewrite
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that call to pass the input as second argument:</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">macro_rules</span><span class="macro">!</span> <span class="ident">method</span> (
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">name</span>:<span class="ident">ident</span><span class="op"><</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">a</span>:<span class="ident">ty</span><span class="op">></span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">self_</span>:<span class="ident">ident</span>, <span class="macro-nonterminal">$</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="op">=</span><span class="op">></span> (
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<span class="kw">fn</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">name</span>( <span class="macro-nonterminal">$</span><span class="macro-nonterminal">self_</span>: <span class="macro-nonterminal">$</span><span class="macro-nonterminal">a</span>, <span class="ident">i</span>: <span class="kw-2">&</span>[<span class="ident">u8</span>] ) <span class="op">-</span><span class="op">></span> <span class="ident">IResult</span><span class="op"><</span><span class="kw-2">&</span>[<span class="ident">u8</span>], <span class="kw-2">&</span>[<span class="ident">u8</span>]<span class="op">></span> {
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<span class="macro-nonterminal">$</span><span class="macro-nonterminal">submac</span><span class="op">!</span>(<span class="ident">i</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">args</span>)<span class="kw-2">*</span>)
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}
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);
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);</pre></div>
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<p>The <code>method!</code> macro is similar to the <code>named!</code> macro in the macros module.
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While <code>named!</code> will create a parser function, <code>method!</code> will create a parser
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method on the struct it is defined in.</p>
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<p>Compared to the <code>named!</code> macro there are a few differences in how they are
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invoked. A <code>method!</code> invocation always has to have the type of <code>self</code>
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declared and it can't be a reference due to Rust's borrow lifetime
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restrictions:</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="comment">// -`self`'s type-</span>
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<span class="macro">method</span><span class="macro">!</span>(<span class="ident">method_name</span><span class="op"><</span> <span class="ident">Parser</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> <span class="op">></span>, ...);</pre></div>
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<p><code>self</code>'s type always comes first.
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The next difference is you have to input the self struct. Due to Rust's
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macro hygiene the macro can't declare it on it's own.</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="comment">// -self-</span>
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<span class="macro">method</span><span class="macro">!</span>(<span class="ident">method_name</span><span class="op"><</span><span class="ident">Parser</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>, <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span>, <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span><span class="op">></span>, <span class="self">self</span>, ...);</pre></div>
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<p>When making a parsing struct with parsing methods, due to the static borrow
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checker,calling any parsing methods on self (or any other parsing struct)
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will cause self to be moved for the rest of the method.To get around this
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restriction all self is moved into the called method and then the called
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method will return self to the caller.</p>
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<p>To call a method on self you need to use the <code>call_m!</code> macro. For example:</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="kw">struct</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> <span class="ident">Parser</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
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<span class="ident">parsed</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span>,
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}
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<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> <span class="ident">Parser</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
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<span class="comment">// Constructor omitted for brevity</span>
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<span class="macro">method</span><span class="macro">!</span>(<span class="ident">take4</span><span class="op"><</span><span class="ident">Parser</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>, <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span>, <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span><span class="op">></span>, <span class="self">self</span>, <span class="macro">take</span><span class="macro">!</span>(<span class="number">4</span>));
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<span class="macro">method</span><span class="macro">!</span>(<span class="ident">caller</span><span class="op"><</span><span class="ident">Parser</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>, <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span>, <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span><span class="op">></span>, <span class="self">self</span>, <span class="macro">call_m</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">take4</span>));
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}</pre></div>
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<p>More complicated combinations still mostly look the same as their <code>named!</code>
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counterparts:</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">method</span><span class="macro">!</span>(<span class="kw">pub</span> <span class="ident">simple_chain</span><span class="op"><</span><span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">Parser</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>, <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span>, <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span><span class="op">></span>, <span class="self">self</span>,
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<span class="macro">do_parse</span><span class="macro">!</span>(
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<span class="macro">call_m</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">tag_abc</span>) <span class="op">></span><span class="op">></span>
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<span class="macro">call_m</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">tag_def</span>) <span class="op">></span><span class="op">></span>
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<span class="macro">call_m</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">tag_ghi</span>) <span class="op">></span><span class="op">></span>
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<span class="ident">last</span>: <span class="macro">map</span><span class="macro">!</span>(<span class="macro">call_m</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">simple_peek</span>), <span class="op">|</span><span class="ident">parsed</span><span class="op">|</span> <span class="ident">sb</span>.<span class="ident">parsed</span> <span class="op">=</span> <span class="ident">parsed</span>) <span class="op">></span><span class="op">></span>
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(<span class="ident">last</span>)
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)
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);</pre></div>
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<p>The three additions to method definitions to remember are:</p>
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<ol>
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<li>Specify <code>self</code>'s type</li>
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<li>Pass <code>self</code> to the macro</li>
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<li>Call parser methods using the <code>call_m!</code> macro.</li>
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</ol>
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