153 lines
6.2 KiB
HTML
153 lines
6.2 KiB
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<meta name="description" content="API documentation for the Rust `reject` macro in crate `syn`.">
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<meta name="keywords" content="rust, rustlang, rust-lang, reject">
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<title>syn::reject - Rust</title>
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things.
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<div class="sidebar-menu">☰</div>
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<p class='location'><a href='index.html'>syn</a></p><script>window.sidebarCurrent = {name: 'reject', ty: 'macro', relpath: ''};</script><script defer src="sidebar-items.js"></script>
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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=''>reject</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#726-731' 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">reject</span> {
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>:<span class="ident">expr</span>,) <span class="op">=></span> { ... };
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}</pre>
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<div class='docblock'><p>Unconditionally fail to parse anything.</p>
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<p>This may be useful in rejecting some arms of a <code>switch!</code> parser.</p>
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<ul>
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<li><strong>Syntax:</strong> <code>reject!()</code></li>
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<li><strong>Output:</strong> never succeeds</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">Item</span>;
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<span class="comment">// Parse any item, except for a module.</span>
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<span class="macro">named</span><span class="macro">!</span>(<span class="ident">almost_any_item</span> <span class="op">-></span> <span class="ident">Item</span>,
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<span class="macro">switch</span><span class="macro">!</span>(<span class="macro">syn</span><span class="macro">!</span>(<span class="ident">Item</span>),
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<span class="ident">Item</span>::<span class="ident">Mod</span>(_) <span class="op">=></span> <span class="macro">reject</span><span class="macro">!</span>()
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<span class="op">|</span>
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<span class="ident">ok</span> <span class="op">=></span> <span class="macro">value</span><span class="macro">!</span>(<span class="ident">ok</span>)
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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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<h2>Keyboard Shortcuts</h2>
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<div class="infos">
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<h2>Search Tricks</h2>
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<p>
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Prefix searches with a type followed by a colon (e.g.
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<code>fn:</code>) to restrict the search to a given type.
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</p>
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<p>
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Accepted types are: <code>fn</code>, <code>mod</code>,
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<code>struct</code>, <code>enum</code>,
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<code>trait</code>, <code>type</code>, <code>macro</code>,
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and <code>const</code>.
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</p>
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<p>
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Search functions by type signature (e.g.
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<code>vec -> usize</code> or <code>* -> vec</code>)
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</div>
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