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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 `quote_spanned` macro in crate `quote`."><meta name="keywords" content="rust, rustlang, rust-lang, quote_spanned"><title>quote::quote_spanned - 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="../light.css" id="themeStyle"><link rel="stylesheet" type="text/css" href="../dark.css" disabled ><link rel="stylesheet" type="text/css" href="../ayu.css" disabled ><script id="default-settings"></script><script src="../storage.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../favicon.svg">
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<link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><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='../quote/index.html'><div class='logo-container rust-logo'><img src='../rust-logo.png' alt='logo'></div></a><div class="sidebar-elems"><p class="location"><a href="index.html">quote</a></p><script>window.sidebarCurrent = {name: "quote_spanned", 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!" aria-haspopup="menu"><img src="../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices" role="menu"></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><span class="help-button">?</span>
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<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/quote/lib.rs.html#581-592" title="goto source code">[src]</a></span><span class="in-band">Macro <a href="index.html">quote</a>::<wbr><a class="macro" href="">quote_spanned</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">quote_spanned</span> {
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">span</span>:<span class="ident">expr</span><span class="op">=</span><span class="op">></span>) <span class="op">=</span><span class="op">></span> { ... };
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">span</span>:<span class="ident">expr</span><span class="op">=</span><span class="op">></span> $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">tt</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>Same as <code>quote!</code>, but applies a given span to all tokens originating within
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the macro invocation.</p>
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<br>
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<h1 id="syntax" class="section-header"><a href="#syntax">Syntax</a></h1>
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<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
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to quote. The span expression should be brief — use a variable for
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anything more than a few characters. There should be no space before the
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<code>=></code> token.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">let</span> <span class="ident">span</span> <span class="op">=</span> <span class="comment">/* ... */</span>;
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<span class="comment">// On one line, use parentheses.</span>
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<span class="kw">let</span> <span class="ident">tokens</span> <span class="op">=</span> <span class="macro">quote_spanned</span><span class="macro">!</span>(<span class="ident">span</span><span class="op">=</span><span class="op">></span> <span class="ident">Box</span>::<span class="ident">into_raw</span>(<span class="ident">Box</span>::<span class="ident">new</span>(#<span class="ident">init</span>)));
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<span class="comment">// On multiple lines, place the span at the top and use braces.</span>
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<span class="kw">let</span> <span class="ident">tokens</span> <span class="op">=</span> <span class="macro">quote_spanned</span><span class="macro">!</span> {<span class="ident">span</span><span class="op">=</span><span class="op">></span>
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<span class="ident">Box</span>::<span class="ident">into_raw</span>(<span class="ident">Box</span>::<span class="ident">new</span>(#<span class="ident">init</span>))
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};</pre></div>
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<p>The lack of space before the <code>=></code> should look jarring to Rust programmers
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and this is intentional. The formatting is designed to be visibly
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off-balance and draw the eye a particular way, due to the span expression
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being evaluated in the context of the procedural macro and the remaining
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tokens being evaluated in the generated code.</p>
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<br>
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<h1 id="hygiene" class="section-header"><a href="#hygiene">Hygiene</a></h1>
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<p>Any interpolated tokens preserve the <code>Span</code> information provided by their
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<code>ToTokens</code> implementation. Tokens that originate within the <code>quote_spanned!</code>
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invocation are spanned with the given span argument.</p>
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<br>
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<h1 id="example" class="section-header"><a href="#example">Example</a></h1>
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<p>The following procedural macro code uses <code>quote_spanned!</code> to assert that a
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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
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safely shared between threads.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">let</span> <span class="ident">ty_span</span> <span class="op">=</span> <span class="ident">ty</span>.<span class="ident">span</span>();
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<span class="kw">let</span> <span class="ident">assert_sync</span> <span class="op">=</span> <span class="macro">quote_spanned</span><span class="macro">!</span> {<span class="ident">ty_span</span><span class="op">=</span><span class="op">></span>
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<span class="kw">struct</span> <span class="ident">_AssertSync</span> <span class="kw">where</span> #<span class="ident">ty</span>: <span class="ident">Sync</span>;
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};</pre></div>
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<p>If the assertion fails, the user will see an error like the following. The
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input span of their type is highlighted in the error.</p>
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<pre><code class="language-text">error[E0277]: the trait bound `*const (): std::marker::Sync` is not satisfied
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--> src/main.rs:10:21
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10 | static ref PTR: *const () = &();
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| ^^^^^^^^^ `*const ()` cannot be shared between threads safely
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</code></pre>
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<p>In this example it is important for the where-clause to be spanned with the
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line/column information of the user's input type so that error messages are
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placed appropriately by the compiler.</p>
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</div></section><section id="search" class="content hidden"></section><section class="footer"></section><script>window.rootPath = "../";window.currentCrate = "quote";</script><script src="../main.js"></script><script defer src="../search-index.js"></script></body></html>
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