| <!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="Define a type that supports parsing and printing a given identifier as if it were a keyword."><meta name="keywords" content="rust, rustlang, rust-lang, custom_keyword"><title>custom_keyword in syn - 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 macro"><!--[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="../syn/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="../syn/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 syn</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">Macro <a href="index.html">syn</a>::<wbr><a class="macro" href="#">custom_keyword</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/syn/custom_keyword.rs.html#90-122">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"><div class="example-wrap"><pre class="rust macro"><code><span class="macro">macro_rules! </span>custom_keyword { |
| (<span class="macro-nonterminal">$ident</span>:ident) => { ... }; |
| }</code></pre></div> |
| </div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Define a type that supports parsing and printing a given identifier as if it |
| were a keyword.</p> |
| <h2 id="usage"><a href="#usage">Usage</a></h2> |
| <p>As a convention, it is recommended that this macro be invoked within a |
| module called <code>kw</code> or <code>keyword</code> and that the resulting parser be invoked |
| with a <code>kw::</code> or <code>keyword::</code> prefix.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">mod </span>kw { |
| <span class="macro">syn::custom_keyword!</span>(whatever); |
| }</code></pre></div> |
| <p>The generated syntax tree node supports the following operations just like |
| any built-in keyword token.</p> |
| <ul> |
| <li> |
| <p><a href="parse/struct.ParseBuffer.html#method.peek">Peeking</a> — <code>input.peek(kw::whatever)</code></p> |
| </li> |
| <li> |
| <p><a href="parse/struct.ParseBuffer.html#method.parse">Parsing</a> — <code>input.parse::<kw::whatever>()?</code></p> |
| </li> |
| <li> |
| <p><a href="../quote/to_tokens/trait.ToTokens.html">Printing</a> — <code>quote!( ... #whatever_token ... )</code></p> |
| </li> |
| <li> |
| <p>Construction from a <a href="../proc_macro2/struct.Span.html"><code>Span</code></a> — <code>let whatever_token = kw::whatever(sp)</code></p> |
| </li> |
| <li> |
| <p>Field access to its span — <code>let sp = whatever_token.span</code></p> |
| </li> |
| </ul> |
| <h2 id="example"><a href="#example">Example</a></h2> |
| <p>This example parses input that looks like <code>bool = true</code> or <code>str = "value"</code>. |
| The key must be either the identifier <code>bool</code> or the identifier <code>str</code>. If |
| <code>bool</code>, the value may be either <code>true</code> or <code>false</code>. If <code>str</code>, the value may |
| be any string literal.</p> |
| <p>The symbols <code>bool</code> and <code>str</code> are not reserved keywords in Rust so these are |
| not considered keywords in the <code>syn::token</code> module. Like any other |
| identifier that is not a keyword, these can be declared as custom keywords |
| by crates that need to use them as such.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>syn::{LitBool, LitStr, <span class="prelude-ty">Result</span>, Token}; |
| <span class="kw">use </span>syn::parse::{Parse, ParseStream}; |
| |
| <span class="kw">mod </span>kw { |
| <span class="macro">syn::custom_keyword!</span>(bool); |
| <span class="macro">syn::custom_keyword!</span>(str); |
| } |
| |
| <span class="kw">enum </span>Argument { |
| Bool { |
| bool_token: kw::bool, |
| eq_token: <span class="macro">Token!</span>[=], |
| value: LitBool, |
| }, |
| Str { |
| str_token: kw::str, |
| eq_token: <span class="macro">Token!</span>[=], |
| value: LitStr, |
| }, |
| } |
| |
| <span class="kw">impl </span>Parse <span class="kw">for </span>Argument { |
| <span class="kw">fn </span>parse(input: ParseStream) -> <span class="prelude-ty">Result</span><<span class="self">Self</span>> { |
| <span class="kw">let </span>lookahead = input.lookahead1(); |
| <span class="kw">if </span>lookahead.peek(kw::bool) { |
| <span class="prelude-val">Ok</span>(Argument::Bool { |
| bool_token: input.parse::<kw::bool>()<span class="question-mark">?</span>, |
| eq_token: input.parse()<span class="question-mark">?</span>, |
| value: input.parse()<span class="question-mark">?</span>, |
| }) |
| } <span class="kw">else if </span>lookahead.peek(kw::str) { |
| <span class="prelude-val">Ok</span>(Argument::Str { |
| str_token: input.parse::<kw::str>()<span class="question-mark">?</span>, |
| eq_token: input.parse()<span class="question-mark">?</span>, |
| value: input.parse()<span class="question-mark">?</span>, |
| }) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">Err</span>(lookahead.error()) |
| } |
| } |
| }</code></pre></div> |
| </div></details></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="syn" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
