Scala Actors Messaging: Ping Pong Example

Question

I am new to Scala and also to Actors. So, I am little bit confused. The first task I worked with is the ping pong example. The code looks as follows

class PingPong(sendTo: Actor, val name: String) extends Actor {
  def act {
   loop {
     receive {
        case x:Int =>
          println(name + " received " + x)
          Thread.sleep(500)
          if (sendTo == null)
            sender ! (x+1)
          else
            sendTo ! (x+1)
      }
    }
  }
} 

object PingPongMain extends App {
  val pong = new PingPong(null, "pong")
  val ping = new PingPong(pong, "ping")
  ping.start()
  pong.start()
  ping ! 0
}

Output is
ping received 0
pong received 1
...

So, how does it get evaluated?
So far, I know .start() calls act().
What happens after then?
ping ! 0 gets called. Does this mean that 0 is send to the address where ping is instantiated? Then does it call act? What if there were more than one method?
But how does pong get called? I mean how does it know where sendTo is?

Also, is it possible to do this with something like val ping/pong = actor {} instead of with extends Actor?

Gangstead Gangstead · Accepted Answer · 2015-03-23T21:24:58

You should pass around ActorRefs not Actors. which are resolved from an ActorSystem
Each actor only needs to define def receive = ... so remove the act and loop ceremony around it
There is no need to start the actor. It will happen automatically when you get the actorRef from the ActorSystem.
Extend the Actor trait. I've never seen it done another way.

Scala Actors Messaging: Ping Pong Example

1 Answers