title: how to send message to all client except sender in rails/actioncable?
body: <p>in socket.io, you can send message to all client except sender like:</p>
  
  <pre><code>socket.broadcast.emit('user connected');
  </code></pre>
  
  <p>but in rails/actioncable, how to do that?</p>
  
  <pre><code>class BoardChannel &lt; ApplicationCable::Channel
     def subscribed
       stream_from "board:#{params[:board]}"
     end
  
     def speak
       # client will call @perform('speak')
       result = do_something()
       # how to send 'result' to all client except sender?
     end
   end
  </code></pre>