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Update and fix
2017-07-14 23:30:16 +00:00
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<h1 class='fqn'><span class='in-band'>Macro <a href='index.html'>synom</a>::<wbr><a class="macro" href=''>switch</a></span><span class='out-of-band'><span id='render-detail'>
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<pre class="rust macro">
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">switch</span> {
(<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> ), $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=&gt;</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">subrule</span>:<span class="macro">ident</span><span class="macro">!</span>( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">args2</span>:<span class="ident">tt</span>)<span class="op">*</span> ))<span class="op">|</span><span class="op">*</span> ) <span class="op">=&gt;</span> { ... };
}</pre>
<div class='docblock'><p>Pattern-match the result of a parser to select which other parser to run.</p>
<ul>
<li><strong>Syntax:</strong> <code>switch!(TARGET, PAT1 =&gt; THEN1 | PAT2 =&gt; THEN2 | ...)</code></li>
<li><strong>Output:</strong> <code>T</code>, the return type of <code>THEN1</code> and <code>THEN2</code> and ...</li>
</ul>
<pre class="rust rust-example-rendered">
<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">syn</span>;
<span class="attribute">#[<span class="ident">macro_use</span>]</span> <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">synom</span>;
<span class="kw">use</span> <span class="ident">syn</span>::{<span class="ident">Ident</span>, <span class="ident">Ty</span>};
<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">parse</span>::{<span class="ident">ident</span>, <span class="ident">ty</span>};
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">enum</span> <span class="ident">UnitType</span> {
<span class="ident">Struct</span> {
<span class="ident">name</span>: <span class="ident">Ident</span>,
},
<span class="ident">Enum</span> {
<span class="ident">name</span>: <span class="ident">Ident</span>,
<span class="ident">variant</span>: <span class="ident">Ident</span>,
},
}
<span class="comment">// Parse a unit struct or enum: either `struct S;` or `enum E { V }`.</span>
<span class="macro">named</span><span class="macro">!</span>(<span class="ident">unit_type</span> <span class="op">-&gt;</span> <span class="ident">UnitType</span>, <span class="macro">do_parse</span><span class="macro">!</span>(
<span class="ident">which</span>: <span class="macro">alt</span><span class="macro">!</span>(<span class="macro">keyword</span><span class="macro">!</span>(<span class="string">&quot;struct&quot;</span>) <span class="op">|</span> <span class="macro">keyword</span><span class="macro">!</span>(<span class="string">&quot;enum&quot;</span>)) <span class="op">&gt;&gt;</span>
<span class="ident">id</span>: <span class="ident">ident</span> <span class="op">&gt;&gt;</span>
<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>),
<span class="string">&quot;struct&quot;</span> <span class="op">=&gt;</span> <span class="macro">map</span><span class="macro">!</span>(
<span class="macro">punct</span><span class="macro">!</span>(<span class="string">&quot;;&quot;</span>),
<span class="kw">move</span> <span class="op">|</span>_<span class="op">|</span> <span class="ident">UnitType</span>::<span class="ident">Struct</span> {
<span class="ident">name</span>: <span class="ident">id</span>,
}
)
<span class="op">|</span>
<span class="string">&quot;enum&quot;</span> <span class="op">=&gt;</span> <span class="macro">map</span><span class="macro">!</span>(
<span class="macro">delimited</span><span class="macro">!</span>(<span class="macro">punct</span><span class="macro">!</span>(<span class="string">&quot;{&quot;</span>), <span class="ident">ident</span>, <span class="macro">punct</span><span class="macro">!</span>(<span class="string">&quot;}&quot;</span>)),
<span class="kw">move</span> <span class="op">|</span><span class="ident">variant</span><span class="op">|</span> <span class="ident">UnitType</span>::<span class="ident">Enum</span> {
<span class="ident">name</span>: <span class="ident">id</span>,
<span class="ident">variant</span>: <span class="ident">variant</span>,
}
)
) <span class="op">&gt;&gt;</span>
(<span class="ident">item</span>)
));
<span class="kw">fn</span> <span class="ident">main</span>() {
<span class="kw">let</span> <span class="ident">input</span> <span class="op">=</span> <span class="string">&quot;struct S;&quot;</span>;
<span class="kw">let</span> <span class="ident">parsed</span> <span class="op">=</span> <span class="ident">unit_type</span>(<span class="ident">input</span>).<span class="ident">expect</span>(<span class="string">&quot;unit struct or enum&quot;</span>);
<span class="macro">println</span><span class="macro">!</span>(<span class="string">&quot;{:?}&quot;</span>, <span class="ident">parsed</span>);
<span class="kw">let</span> <span class="ident">input</span> <span class="op">=</span> <span class="string">&quot;enum E { V }&quot;</span>;
<span class="kw">let</span> <span class="ident">parsed</span> <span class="op">=</span> <span class="ident">unit_type</span>(<span class="ident">input</span>).<span class="ident">expect</span>(<span class="string">&quot;unit struct or enum&quot;</span>);
<span class="macro">println</span><span class="macro">!</span>(<span class="string">&quot;{:?}&quot;</span>, <span class="ident">parsed</span>);
}</pre>
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