mentat/syn/fn.parse.html
2018-08-22 17:04:13 +00:00

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<h1 class='fqn'><span class='in-band'>Function <a href='index.html'>syn</a>::<wbr><a class="fn" href=''>parse</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/lib.rs.html#637-642' title='goto source code'>[src]</a></span></h1>
<pre class='rust fn'>pub fn parse&lt;T&gt;(tokens: <a class="struct" href="https://doc.rust-lang.org/nightly/proc_macro/struct.TokenStream.html" title="struct proc_macro::TokenStream">TokenStream</a>) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a>&lt;T, <a class="struct" href="../syn/synom/struct.ParseError.html" title="struct syn::synom::ParseError">ParseError</a>&gt; <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;T: <a class="trait" href="../syn/synom/trait.Synom.html" title="trait syn::synom::Synom">Synom</a>,&nbsp;</span></pre><div class='docblock'><p>Parse tokens of source code into the chosen syntax tree node.</p>
<p>This is preferred over parsing a string because tokens are able to preserve
information about where in the user's code they were originally written (the
&quot;span&quot; of the token), possibly allowing the compiler to produce better error
messages.</p>
<p>This function parses a <code>proc_macro::TokenStream</code> which is the type used for
interop with the compiler in a procedural macro. To parse a
<code>proc_macro2::TokenStream</code>, use <a href="fn.parse2.html"><code>syn::parse2</code></a> instead.</p>
<p><em>This function is available if Syn is built with both the <code>&quot;parsing&quot;</code> and
<code>&quot;proc-macro&quot;</code> features.</em></p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">proc_macro</span>;
<span class="kw">use</span> <span class="ident">proc_macro</span>::<span class="ident">TokenStream</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">DeriveInput</span>;
<span class="attribute">#[<span class="ident">proc_macro_derive</span>(<span class="ident">MyMacro</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">my_macro</span>(<span class="ident">input</span>: <span class="ident">TokenStream</span>) <span class="op">-&gt;</span> <span class="ident">TokenStream</span> {
<span class="comment">// Parse the tokens into a syntax tree</span>
<span class="kw">let</span> <span class="ident">ast</span>: <span class="ident">DeriveInput</span> <span class="op">=</span> <span class="ident">syn</span>::<span class="ident">parse</span>(<span class="ident">input</span>).<span class="ident">unwrap</span>();
<span class="comment">// Build the output, possibly using quasi-quotation</span>
<span class="kw">let</span> <span class="ident">expanded</span> <span class="op">=</span> <span class="macro">quote</span><span class="macro">!</span> {
<span class="comment">/* ... */</span>
};
<span class="comment">// Convert into a token stream and return it</span>
<span class="ident">expanded</span>.<span class="ident">into</span>()
}</pre>
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