_actor</a><span class="special">&lt;</span> <span class="identifier">ChannelT</span><span class="special">,</span> <span class="identifier">ChannelFallbackT</span><span class="special">,</span> <span class="identifier">ChannelTagT</span><span class="special">,</span> <span class="identifier">ActorT</span> <span class="special">&gt;</span> <span class="keyword">const</span> <span class="special">&amp;</span> channel_placeholder<span class="special">,</span> 
                          <span class="identifier"