| <!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="Same as `quote!`, but applies a given span to all tokens originating within the macro invocation."><meta name="keywords" content="rust, rustlang, rust-lang, quote_spanned"><title>quote_spanned in quote - 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="../quote/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="../quote/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 quote</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">quote</a>::<wbr><a class="macro" href="#">quote_spanned</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/quote/lib.rs.html#620-624">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>quote_spanned { |
| (<span class="macro-nonterminal">$span</span>:expr=> $(<span class="macro-nonterminal">$tt</span>:tt)<span class="kw-2">*</span>) => { ... }; |
| }</code></pre></div> |
| </div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Same as <code>quote!</code>, but applies a given span to all tokens originating within |
| the macro invocation.</p> |
| <br> |
| <h2 id="syntax"><a href="#syntax">Syntax</a></h2> |
| <p>A span expression of type <a href="https://docs.rs/proc-macro2/1.0/proc_macro2/struct.Span.html"><code>Span</code></a>, followed by <code>=></code>, followed by the tokens |
| to quote. The span expression should be brief — use a variable for |
| anything more than a few characters. There should be no space before the |
| <code>=></code> token.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let </span>span = <span class="comment">/* ... */</span>; |
| |
| <span class="comment">// On one line, use parentheses. |
| </span><span class="kw">let </span>tokens = <span class="macro">quote_spanned!</span>(span=> Box::into_raw(Box::new(#init))); |
| |
| <span class="comment">// On multiple lines, place the span at the top and use braces. |
| </span><span class="kw">let </span>tokens = <span class="macro">quote_spanned! </span>{span=> |
| Box::into_raw(Box::new(#init)) |
| };</code></pre></div> |
| <p>The lack of space before the <code>=></code> should look jarring to Rust programmers |
| and this is intentional. The formatting is designed to be visibly |
| off-balance and draw the eye a particular way, due to the span expression |
| being evaluated in the context of the procedural macro and the remaining |
| tokens being evaluated in the generated code.</p> |
| <br> |
| <h2 id="hygiene"><a href="#hygiene">Hygiene</a></h2> |
| <p>Any interpolated tokens preserve the <code>Span</code> information provided by their |
| <code>ToTokens</code> implementation. Tokens that originate within the <code>quote_spanned!</code> |
| invocation are spanned with the given span argument.</p> |
| <br> |
| <h2 id="example"><a href="#example">Example</a></h2> |
| <p>The following procedural macro code uses <code>quote_spanned!</code> to assert that a |
| particular Rust type implements the <a href="https://doc.rust-lang.org/std/marker/trait.Sync.html"><code>Sync</code></a> trait so that references can be |
| safely shared between threads.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let </span>ty_span = ty.span(); |
| <span class="kw">let </span>assert_sync = <span class="macro">quote_spanned! </span>{ty_span=> |
| <span class="kw">struct </span>_AssertSync <span class="kw">where </span>#ty: Sync; |
| };</code></pre></div> |
| <p>If the assertion fails, the user will see an error like the following. The |
| input span of their type is highlighted in the error.</p> |
| <div class="example-wrap"><pre class="language-text"><code>error[E0277]: the trait bound `*const (): std::marker::Sync` is not satisfied |
| --> src/main.rs:10:21 |
| | |
| 10 | static ref PTR: *const () = &(); |
| | ^^^^^^^^^ `*const ()` cannot be shared between threads safely</code></pre></div> |
| <p>In this example it is important for the where-clause to be spanned with the |
| line/column information of the user’s input type so that error messages are |
| placed appropriately by the compiler.</p> |
| </div></details></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="quote" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
