al">,</span> <span class="keyword">bool</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>

  <span class="comment">// <a class="link" href="channel_visitor.html#idp36953328-bb">public member functions</a></span>
  <span class="identifier">result_type</span> <a class="link" href="channel_visitor.html#idp36953888-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class=