204 lines
11 KiB
HTML
204 lines
11 KiB
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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=''>value</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#693-697' 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">value</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">res</span>:<span class="ident">expr</span>) <span class="op">=></span> { ... };
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}</pre>
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<div class='docblock'><p>Produce the given value without parsing anything.</p>
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<p>This can be needed where you have an existing parsed value but a parser
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macro's syntax expects you to provide a submacro, such as in the first
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argument of <a href="macro.switch.html"><code>switch!</code></a> or one of the branches of <a href="macro.alt.html"><code>alt!</code></a>.</p>
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<ul>
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<li><strong>Syntax:</strong> <code>value!(VALUE)</code></li>
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<li><strong>Output:</strong> <code>VALUE</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">Ident</span>;
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<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">token</span>::<span class="ident">Brace</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">/// Parse a unit struct or enum: either `struct S;` or `enum E { V }`.</span>
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<span class="kw">enum</span> <span class="ident">UnitType</span> {
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<span class="ident">Struct</span> {
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<span class="ident">struct_token</span>: <span class="macro">Token</span><span class="macro">!</span>[<span class="kw">struct</span>],
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<span class="ident">name</span>: <span class="ident">Ident</span>,
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<span class="ident">semi_token</span>: <span class="macro">Token</span><span class="macro">!</span>[;],
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},
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<span class="ident">Enum</span> {
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<span class="ident">enum_token</span>: <span class="macro">Token</span><span class="macro">!</span>[<span class="kw">enum</span>],
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<span class="ident">name</span>: <span class="ident">Ident</span>,
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<span class="ident">brace_token</span>: <span class="ident">Brace</span>,
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<span class="ident">variant</span>: <span class="ident">Ident</span>,
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},
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}
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<span class="kw">enum</span> <span class="ident">StructOrEnum</span> {
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<span class="ident">Struct</span>(<span class="macro">Token</span><span class="macro">!</span>[<span class="kw">struct</span>]),
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<span class="ident">Enum</span>(<span class="macro">Token</span><span class="macro">!</span>[<span class="kw">enum</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">StructOrEnum</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">alt</span><span class="macro">!</span>(
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<span class="macro">keyword</span><span class="macro">!</span>(<span class="kw">struct</span>) <span class="op">=></span> { <span class="ident">StructOrEnum</span>::<span class="ident">Struct</span> }
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<span class="op">|</span>
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<span class="macro">keyword</span><span class="macro">!</span>(<span class="kw">enum</span>) <span class="op">=></span> { <span class="ident">StructOrEnum</span>::<span class="ident">Enum</span> }
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));
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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">UnitType</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="ident">which</span>: <span class="macro">syn</span><span class="macro">!</span>(<span class="ident">StructOrEnum</span>) <span class="op">>></span>
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<span class="ident">name</span>: <span class="macro">syn</span><span class="macro">!</span>(<span class="ident">Ident</span>) <span class="op">>></span>
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<span class="ident">item</span>: <span class="macro">switch</span><span class="macro">!</span>(<span class="macro">value</span><span class="macro">!</span>(<span class="ident">which</span>),
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<span class="ident">StructOrEnum</span>::<span class="ident">Struct</span>(<span class="ident">struct_token</span>) <span class="op">=></span> <span class="macro">map</span><span class="macro">!</span>(
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<span class="macro">punct</span><span class="macro">!</span>(;),
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<span class="op">|</span><span class="ident">semi_token</span><span class="op">|</span> <span class="ident">UnitType</span>::<span class="ident">Struct</span> {
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<span class="ident">struct_token</span>,
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<span class="ident">name</span>,
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<span class="ident">semi_token</span>,
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}
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)
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<span class="op">|</span>
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<span class="ident">StructOrEnum</span>::<span class="ident">Enum</span>(<span class="ident">enum_token</span>) <span class="op">=></span> <span class="macro">map</span><span class="macro">!</span>(
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<span class="macro">braces</span><span class="macro">!</span>(<span class="macro">syn</span><span class="macro">!</span>(<span class="ident">Ident</span>)),
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<span class="op">|</span>(<span class="ident">brace_token</span>, <span class="ident">variant</span>)<span class="op">|</span> <span class="ident">UnitType</span>::<span class="ident">Enum</span> {
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<span class="ident">enum_token</span>,
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<span class="ident">name</span>,
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<span class="ident">brace_token</span>,
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<span class="ident">variant</span>,
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}
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)
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) <span class="op">>></span>
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(<span class="ident">item</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>Search Tricks</h2>
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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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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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Search functions by type signature (e.g.
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<code>vec -> usize</code> or <code>* -> vec</code>)
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