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macro.format_ident.html
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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>quote::format_ident - 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><script src="../crates.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../favicon.svg">
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<a id="settings-menu" href="../settings.html"><img src="../wheel.svg" width="18" height="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class="fqn"><span class="in-band">Macro <a href="index.html">quote</a>::<wbr><a class="macro" href="">format_ident</a></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#110-124" title="goto source code">[src]</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><div class="example-wrap"><pre class="rust macro">
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">format_ident</span> {
(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">fmt</span>:<span class="ident">expr</span>) <span class="op">=</span><span class="op">></span> { ... };
(<span class="macro-nonterminal">$</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>) <span class="op">=</span><span class="op">></span> { ... };
}</pre></div>
</div><div class="docblock"><p>Formatting macro for constructing <code>Ident</code>s.</p>
<br>
<h1 id="syntax" class="section-header"><a href="#syntax">Syntax</a></h1>
<p>Syntax is copied from the <a href="https://doc.rust-lang.org/nightly/alloc/macro.format.html" title="format!"><code>format!</code></a> macro, supporting both positional and
named arguments.</p>
<p>Only a limited set of formatting traits are supported. The current mapping
of format types to traits is:</p>
<ul>
<li><code>{}</code> ⇒ [<code>IdentFragment</code>]</li>
<li><code>{:o}</code> ⇒ <a href="https://doc.rust-lang.org/nightly/core/fmt/trait.Octal.html"><code>Octal</code></a></li>
<li><code>{:x}</code> ⇒ <a href="https://doc.rust-lang.org/nightly/core/fmt/trait.LowerHex.html"><code>LowerHex</code></a></li>
<li><code>{:X}</code> ⇒ <a href="https://doc.rust-lang.org/nightly/core/fmt/trait.UpperHex.html"><code>UpperHex</code></a></li>
<li><code>{:b}</code> ⇒ <a href="https://doc.rust-lang.org/nightly/core/fmt/trait.Binary.html"><code>Binary</code></a></li>
</ul>
<p>See <a href="https://doc.rust-lang.org/nightly/alloc/fmt/index.html" title="std::fmt"><code>std::fmt</code></a> for more information.</p>
<br>
<h1 id="identfragment" class="section-header"><a href="#identfragment">IdentFragment</a></h1>
<p>Unlike <code>format!</code>, this macro uses the [<code>IdentFragment</code>] formatting trait by
default. This trait is like <code>Display</code>, with a few differences:</p>
<ul>
<li><code>IdentFragment</code> is only implemented for a limited set of types, such as
unsigned integers and strings.</li>
<li><a href="../proc_macro2/struct.Ident.html"><code>Ident</code></a> arguments will have their <code>r#</code> prefixes stripped, if present.</li>
</ul>
<br>
<h1 id="hygiene" class="section-header"><a href="#hygiene">Hygiene</a></h1>
<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
identifier, falling back to <a href="../proc_macro2/struct.Span.html#method.call_site"><code>Span::call_site</code></a> when no identifiers are
provided.</p>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="comment">// If `ident` is an Ident, the span of `my_ident` will be inherited from it.</span>
<span class="kw">let</span> <span class="ident">my_ident</span> <span class="op">=</span> <span class="macro">format_ident</span><span class="macro">!</span>(<span class="string">"My{}{}"</span>, <span class="ident">ident</span>, <span class="string">"IsCool"</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">my_ident</span>, <span class="string">"MyIdentIsCool"</span>);</pre></div>
<p>Alternatively, the span can be overridden by passing the <code>span</code> named
argument.</p>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">let</span> <span class="ident">my_span</span> <span class="op">=</span> <span class="comment">/* ... */</span>;
<span class="macro">format_ident</span><span class="macro">!</span>(<span class="string">"MyIdent"</span>, <span class="ident">span</span> <span class="op">=</span> <span class="ident">my_span</span>);</pre></div>
<p><br></p>
<h1 id="panics" class="section-header"><a href="#panics">Panics</a></h1>
<p>This method will panic if the resulting formatted string is not a valid
identifier.</p>
<br>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>Composing raw and non-raw identifiers:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">let</span> <span class="ident">my_ident</span> <span class="op">=</span> <span class="macro">format_ident</span><span class="macro">!</span>(<span class="string">"My{}"</span>, <span class="string">"Ident"</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">my_ident</span>, <span class="string">"MyIdent"</span>);
<span class="kw">let</span> <span class="ident">raw</span> <span class="op">=</span> <span class="macro">format_ident</span><span class="macro">!</span>(<span class="string">"r#Raw"</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">raw</span>, <span class="string">"r#Raw"</span>);
<span class="kw">let</span> <span class="ident">my_ident_raw</span> <span class="op">=</span> <span class="macro">format_ident</span><span class="macro">!</span>(<span class="string">"{}Is{}"</span>, <span class="ident">my_ident</span>, <span class="ident">raw</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">my_ident_raw</span>, <span class="string">"MyIdentIsRaw"</span>);</pre></div>
<p>Integer formatting options:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">let</span> <span class="ident">num</span>: <span class="ident">u32</span> <span class="op">=</span> <span class="number">10</span>;
<span class="kw">let</span> <span class="ident">decimal</span> <span class="op">=</span> <span class="macro">format_ident</span><span class="macro">!</span>(<span class="string">"Id_{}"</span>, <span class="ident">num</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">decimal</span>, <span class="string">"Id_10"</span>);
<span class="kw">let</span> <span class="ident">octal</span> <span class="op">=</span> <span class="macro">format_ident</span><span class="macro">!</span>(<span class="string">"Id_{:o}"</span>, <span class="ident">num</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">octal</span>, <span class="string">"Id_12"</span>);
<span class="kw">let</span> <span class="ident">binary</span> <span class="op">=</span> <span class="macro">format_ident</span><span class="macro">!</span>(<span class="string">"Id_{:b}"</span>, <span class="ident">num</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">binary</span>, <span class="string">"Id_1010"</span>);
<span class="kw">let</span> <span class="ident">lower_hex</span> <span class="op">=</span> <span class="macro">format_ident</span><span class="macro">!</span>(<span class="string">"Id_{:x}"</span>, <span class="ident">num</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">lower_hex</span>, <span class="string">"Id_a"</span>);
<span class="kw">let</span> <span class="ident">upper_hex</span> <span class="op">=</span> <span class="macro">format_ident</span><span class="macro">!</span>(<span class="string">"Id_{:X}"</span>, <span class="ident">num</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">upper_hex</span>, <span class="string">"Id_A"</span>);</pre></div>
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