emplate</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">&gt;</span> 
<span class="keyword">struct</span> <a class="link" href="result.html" title="Struct template result">result</a> <span class="special">{</span>
  <span class="comment">// types</span>
  <span class="keyword">typedef</span> <em class="replaceable"><code><span class="identifier">unspecified</span></code></em> <a name="boost.proto.extends.result.type"></a><span class="identifier">typ