171 lines
8.1 KiB
HTML
171 lines
8.1 KiB
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<!DOCTYPE html>
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<meta name="keywords" content="rust, rustlang, rust-lang, option">
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<title>syn::option - Rust</title>
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<p class='location'><a href='index.html'>syn</a></p><script>window.sidebarCurrent = {name: 'option', ty: 'macro', relpath: ''};</script><script defer src="sidebar-items.js"></script>
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autocomplete="off"
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placeholder="Click or press ‘S’ to search, ‘?’ for more options…"
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type="search">
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<section id='main' class="content">
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<h1 class='fqn'><span class='in-band'>Macro <a href='index.html'>syn</a>::<wbr><a class="macro" href=''>option</a></span><span class='out-of-band'><span id='render-detail'>
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<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
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[<span class='inner'>−</span>]
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</a>
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</span><a class='srclink' href='../src/syn/parsers.rs.html#1118-1131' title='goto source code'>[src]</a></span></h1>
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<pre class="rust macro">
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<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">option</span> {
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">submac</span>:<span class="macro">ident</span><span class="macro">!</span>( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">args</span>:<span class="ident">tt</span>)<span class="op">*</span> )) <span class="op">=></span> { ... };
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span>) <span class="op">=></span> { ... };
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}</pre>
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<div class='docblock'><p>Turn a failed parse into <code>None</code> and a successful parse into <code>Some</code>.</p>
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<p>A failed parse consumes none of the input.</p>
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<ul>
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<li><strong>Syntax:</strong> <code>option!(THING)</code></li>
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<li><strong>Output:</strong> <code>Option<THING></code></li>
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</ul>
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<pre class="rust rust-example-rendered">
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<span class="attribute">#[<span class="ident">macro_use</span>]</span>
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<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">syn</span>;
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<span class="kw">use</span> <span class="ident">syn</span>::{<span class="ident">Label</span>, <span class="ident">Block</span>};
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<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">synom</span>::<span class="ident">Synom</span>;
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<span class="doccomment">/// Parses a Rust loop. Equivalent to syn::ExprLoop.</span>
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<span class="doccomment">///</span>
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<span class="doccomment">/// Examples:</span>
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<span class="doccomment">/// loop { println!("y"); }</span>
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<span class="doccomment">/// 'x: loop { break 'x; }</span>
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<span class="kw">struct</span> <span class="ident">ExprLoop</span> {
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<span class="ident">label</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Label</span><span class="op">></span>,
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<span class="ident">loop_token</span>: <span class="macro">Token</span><span class="macro">!</span>[<span class="kw">loop</span>],
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<span class="ident">body</span>: <span class="ident">Block</span>,
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}
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<span class="kw">impl</span> <span class="ident">Synom</span> <span class="kw">for</span> <span class="ident">ExprLoop</span> {
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<span class="macro">named</span><span class="macro">!</span>(<span class="ident">parse</span> <span class="op">-></span> <span class="self">Self</span>, <span class="macro">do_parse</span><span class="macro">!</span>(
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<span class="comment">// Loop may or may not have a label.</span>
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<span class="ident">label</span>: <span class="macro">option</span><span class="macro">!</span>(<span class="macro">syn</span><span class="macro">!</span>(<span class="ident">Label</span>)) <span class="op">>></span>
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<span class="ident">loop_token</span>: <span class="macro">keyword</span><span class="macro">!</span>(<span class="kw">loop</span>) <span class="op">>></span>
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<span class="ident">body</span>: <span class="macro">syn</span><span class="macro">!</span>(<span class="ident">Block</span>) <span class="op">>></span>
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(<span class="ident">ExprLoop</span> {
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<span class="ident">label</span>,
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<span class="ident">loop_token</span>,
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<span class="ident">body</span>,
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})
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));
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}</pre>
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<p><em>This macro is available if Syn is built with the <code>"parsing"</code> feature.</em></p>
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</div></section>
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Accepted types are: <code>fn</code>, <code>mod</code>,
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Search functions by type signature (e.g.
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