/span> <span class="keyword">typename</span> <span class="special">&gt;</span> <span class="keyword">class</span> ActorT<span class="special">&gt;</span> 
  <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">extract</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">expressions</span><span class="special">::</span><span class="identifier">attribute_keyword</span><span class="special">&lt;</span> <span class="id