mentat/syn/macro.parse_quote.html

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2018-08-22 17:04:13 +00:00
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<h1 class='fqn'><span class='in-band'>Macro <a href='index.html'>syn</a>::<wbr><a class="macro" href=''>parse_quote</a></span><span class='out-of-band'><span id='render-detail'>
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[<span class='inner'>&#x2212;</span>]
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</span><a class='srclink' href='../src/syn/parse_quote.rs.html#82-86' title='goto source code'>[src]</a></span></h1>
<pre class="rust macro">
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">parse_quote</span> {
($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">tt</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=&gt;</span> { ... };
}</pre>
<div class='docblock'><p>Quasi-quotation macro that accepts input like the <a href="https://docs.rs/quote/0.4/quote/index.html"><code>quote!</code></a> macro but uses
type inference to figure out a return type for those tokens.</p>
<p>The return type can be any syntax tree node that implements the <a href="synom/trait.Synom.html"><code>Synom</code></a>
trait.</p>
<pre class="rust rust-example-rendered">
<span class="attribute">#[<span class="ident">macro_use</span>]</span>
<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">quote</span>;
<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">Stmt</span>;
<span class="kw">fn</span> <span class="ident">main</span>() {
<span class="kw">let</span> <span class="ident">name</span> <span class="op">=</span> <span class="macro">quote</span><span class="macro">!</span>(<span class="ident">v</span>);
<span class="kw">let</span> <span class="ident">ty</span> <span class="op">=</span> <span class="macro">quote</span><span class="macro">!</span>(<span class="ident">u8</span>);
<span class="kw">let</span> <span class="ident">stmt</span>: <span class="ident">Stmt</span> <span class="op">=</span> <span class="macro">parse_quote</span><span class="macro">!</span> {
<span class="kw">let</span> #<span class="ident">name</span>: #<span class="ident">ty</span> <span class="op">=</span> <span class="ident">Default</span>::<span class="ident">default</span>();
};
<span class="macro">println</span><span class="macro">!</span>(<span class="string">&quot;{:#?}&quot;</span>, <span class="ident">stmt</span>);
}</pre>
<p><em>This macro is available if Syn is built with the <code>&quot;parsing&quot;</code> feature,
although interpolation of syntax tree nodes into the quoted tokens is only
supported if Syn is built with the <code>&quot;printing&quot;</code> feature as well.</em></p>
<h1 id="example" class="section-header"><a href="#example">Example</a></h1>
<p>The following helper function adds a bound <code>T: HeapSize</code> to every type
parameter <code>T</code> in the input generics.</p>
<pre class="rust rust-example-rendered">
<span class="comment">// Add a bound `T: HeapSize` to every type parameter T.</span>
<span class="kw">fn</span> <span class="ident">add_trait_bounds</span>(<span class="kw-2">mut</span> <span class="ident">generics</span>: <span class="ident">Generics</span>) <span class="op">-&gt;</span> <span class="ident">Generics</span> {
<span class="kw">for</span> <span class="ident">param</span> <span class="kw">in</span> <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">generics</span>.<span class="ident">params</span> {
<span class="kw">if</span> <span class="kw">let</span> <span class="ident">GenericParam</span>::<span class="ident">Type</span>(<span class="kw-2">ref</span> <span class="kw-2">mut</span> <span class="ident">type_param</span>) <span class="op">=</span> <span class="kw-2">*</span><span class="ident">param</span> {
<span class="ident">type_param</span>.<span class="ident">bounds</span>.<span class="ident">push</span>(<span class="macro">parse_quote</span><span class="macro">!</span>(<span class="ident">HeapSize</span>));
}
}
<span class="ident">generics</span>
}</pre>
<h1 id="special-cases" class="section-header"><a href="#special-cases">Special cases</a></h1>
<p>This macro can parse the following additional types as a special case even
though they do not implement the <code>Synom</code> trait.</p>
<ul>
<li><a href="struct.Attribute.html"><code>Attribute</code></a> — parses one attribute, allowing either outer like <code>#[...]</code>
or inner like <code>#![...]</code></li>
<li><a href="punctuated/struct.Punctuated.html"><code>Punctuated&lt;T, P&gt;</code></a> — parses zero or more <code>T</code> separated by punctuation
<code>P</code> with optional trailing punctuation</li>
</ul>
<h1 id="panics" class="section-header"><a href="#panics">Panics</a></h1>
<p>Panics if the tokens fail to parse as the expected syntax tree type. The
caller is responsible for ensuring that the input tokens are syntactically
valid.</p>
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