title: What does a single apostrophe mean in Scala?
body: <p>In this slide show on <a href="http://lamp.epfl.ch/~phaller/doc/ScalaActors.pdf" rel="noreferrer">ScalaActors.pdf</a> what does the single quote indicate when the message is sent to the pong actor? </p>
  
  <pre><code>class Ping(count: int, pong: Pong) extends Actor {
  def act() {
     pong ! 'Ping // what does the single quote indicate???
        receive {
           case 'Pong =&gt;
        }
     }
  }
  </code></pre>