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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="Formatting macro for constructing `Ident`s."><meta name="keywords" content="rust, rustlang, rust-lang, format_ident"><title>format_ident 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" type="text/css" href="../normalize.css"><link rel="stylesheet" type="text/css" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../ayu.css" disabled><link rel="stylesheet" type="text/css" href="../dark.css" disabled><link rel="stylesheet" type="text/css" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script src="../crates.js"></script><script defer src="../main.js"></script>
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</a><div class="sidebar-elems"><h2 class="location">Other items in<br><a href="index.html">quote</a></h2><div id="sidebar-vars" data-name="format_ident" data-ty="macro" data-relpath=""></div><script defer src="sidebar-items.js"></script></div></nav><main><div class="width-limiter"><div class="sub-container"><a class="sub-logo-container" href="../quote/index.html"><img class="rust-logo" src="../rust-logo.png" alt="logo"></a><nav class="sub"><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu" title="themes"><img width="18" height="18" alt="Pick another theme!" src="../brush.svg"></button><div id="theme-choices" role="menu"></div></div><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" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><button type="button" id="help-button" title="help">?</button><a id="settings-menu" href="../settings.html" title="settings"><img width="18" height="18" alt="Change settings" src="../wheel.svg"></a></div></form></nav></div><section id="main-content" class="content"><h1 class="fqn"><span class="in-band">Macro <a href="index.html">quote</a>::<wbr><a class="macro" href="#">format_ident</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></span><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/format.rs.html#111-125" title="goto source code">[src]</a></span></h1><div class="docblock item-decl"><div class="example-wrap"><pre class="rust macro"><code><span class="macro">macro_rules!</span> <span class="ident">format_ident</span> {
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">fmt</span> : <span class="ident">expr</span>) => { ... };
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">fmt</span> : <span class="ident">expr</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">rest</span> : <span class="ident">tt</span>) <span class="kw-2">*</span>) => { ... };
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}</code></pre></div>
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</div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Formatting macro for constructing <code>Ident</code>s.</p>
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<br>
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<h2 id="syntax" class="section-header"><a href="#syntax">Syntax</a></h2>
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<p>Syntax is copied from the <a href="https://doc.rust-lang.org/1.59.0/alloc/macro.format.html" title="format!"><code>format!</code></a> macro, supporting both positional and
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named arguments.</p>
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<p>Only a limited set of formatting traits are supported. The current mapping
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of format types to traits is:</p>
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<ul>
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<li><code>{}</code> ⇒ <a href="trait.IdentFragment.html"><code>IdentFragment</code></a></li>
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<li><code>{:o}</code> ⇒ <a href="https://doc.rust-lang.org/1.59.0/core/fmt/trait.Octal.html"><code>Octal</code></a></li>
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<li><code>{:x}</code> ⇒ <a href="https://doc.rust-lang.org/1.59.0/core/fmt/trait.LowerHex.html"><code>LowerHex</code></a></li>
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<li><code>{:X}</code> ⇒ <a href="https://doc.rust-lang.org/1.59.0/core/fmt/trait.UpperHex.html"><code>UpperHex</code></a></li>
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<li><code>{:b}</code> ⇒ <a href="https://doc.rust-lang.org/1.59.0/core/fmt/trait.Binary.html"><code>Binary</code></a></li>
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</ul>
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<p>See <a href="https://doc.rust-lang.org/1.59.0/alloc/fmt/index.html" title="std::fmt"><code>std::fmt</code></a> for more information.</p>
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<br>
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<h2 id="identfragment" class="section-header"><a href="#identfragment">IdentFragment</a></h2>
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<p>Unlike <code>format!</code>, this macro uses the <a href="trait.IdentFragment.html"><code>IdentFragment</code></a> formatting trait by
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default. This trait is like <code>Display</code>, with a few differences:</p>
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<ul>
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<li><code>IdentFragment</code> is only implemented for a limited set of types, such as
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unsigned integers and strings.</li>
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<li><a href="../proc_macro2/struct.Ident.html"><code>Ident</code></a> arguments will have their <code>r#</code> prefixes stripped, if present.</li>
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</ul>
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<br>
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<h2 id="hygiene" class="section-header"><a href="#hygiene">Hygiene</a></h2>
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<p>The <a href="../proc_macro2/struct.Span.html"><code>Span</code></a> of the first <code>Ident</code> argument is used as the span of the final
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identifier, falling back to <a href="../proc_macro2/struct.Span.html#method.call_site"><code>Span::call_site</code></a> when no identifiers are
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provided.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="comment">// If `ident` is an Ident, the span of `my_ident` will be inherited from it.</span>
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<span class="kw">let</span> <span class="ident">my_ident</span> <span class="op">=</span> <span class="macro">format_ident!</span>(<span class="string">"My{}{}"</span>, <span class="ident">ident</span>, <span class="string">"IsCool"</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">my_ident</span>, <span class="string">"MyIdentIsCool"</span>);</code></pre></div>
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<p>Alternatively, the span can be overridden by passing the <code>span</code> named
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argument.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let</span> <span class="ident">my_span</span> <span class="op">=</span> <span class="comment">/* ... */</span>;
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<span class="macro">format_ident!</span>(<span class="string">"MyIdent"</span>, <span class="ident">span</span> <span class="op">=</span> <span class="ident">my_span</span>);</code></pre></div>
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<p><br></p>
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<h2 id="panics" class="section-header"><a href="#panics">Panics</a></h2>
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<p>This method will panic if the resulting formatted string is not a valid
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identifier.</p>
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<br>
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<h2 id="examples" class="section-header"><a href="#examples">Examples</a></h2>
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<p>Composing raw and non-raw identifiers:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let</span> <span class="ident">my_ident</span> <span class="op">=</span> <span class="macro">format_ident!</span>(<span class="string">"My{}"</span>, <span class="string">"Ident"</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">my_ident</span>, <span class="string">"MyIdent"</span>);
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<span class="kw">let</span> <span class="ident">raw</span> <span class="op">=</span> <span class="macro">format_ident!</span>(<span class="string">"r#Raw"</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">raw</span>, <span class="string">"r#Raw"</span>);
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<span class="kw">let</span> <span class="ident">my_ident_raw</span> <span class="op">=</span> <span class="macro">format_ident!</span>(<span class="string">"{}Is{}"</span>, <span class="ident">my_ident</span>, <span class="ident">raw</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">my_ident_raw</span>, <span class="string">"MyIdentIsRaw"</span>);</code></pre></div>
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<p>Integer formatting options:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let</span> <span class="ident">num</span>: <span class="ident">u32</span> <span class="op">=</span> <span class="number">10</span>;
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<span class="kw">let</span> <span class="ident">decimal</span> <span class="op">=</span> <span class="macro">format_ident!</span>(<span class="string">"Id_{}"</span>, <span class="ident">num</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">decimal</span>, <span class="string">"Id_10"</span>);
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<span class="kw">let</span> <span class="ident">octal</span> <span class="op">=</span> <span class="macro">format_ident!</span>(<span class="string">"Id_{:o}"</span>, <span class="ident">num</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">octal</span>, <span class="string">"Id_12"</span>);
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<span class="kw">let</span> <span class="ident">binary</span> <span class="op">=</span> <span class="macro">format_ident!</span>(<span class="string">"Id_{:b}"</span>, <span class="ident">num</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">binary</span>, <span class="string">"Id_1010"</span>);
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<span class="kw">let</span> <span class="ident">lower_hex</span> <span class="op">=</span> <span class="macro">format_ident!</span>(<span class="string">"Id_{:x}"</span>, <span class="ident">num</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">lower_hex</span>, <span class="string">"Id_a"</span>);
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<span class="kw">let</span> <span class="ident">upper_hex</span> <span class="op">=</span> <span class="macro">format_ident!</span>(<span class="string">"Id_{:X}"</span>, <span class="ident">num</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">upper_hex</span>, <span class="string">"Id_A"</span>);</code></pre></div>
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