pubsub.scala

  case class GreetingEvent(msg: String)

  class Greeter extends Publisher[GreetingEvent] {
    def greet(msg:String) = {
      println("Firing event")
      publish(GreetingEvent(msg))
    }
  }

  class GreetingSubscriber(name: String)
      extends Subscriber[GreetingEvent, Publisher[GreetingEvent]] {
    override def notify(source: Publisher[GreetingEvent], event: GreetingEvent) {
      println(s"$name received: ${event.msg}")
    }
  }

  val greeter = new Greeter()
  val s1 = new GreetingSubscriber("Subscriber 1")
  val s2 = new GreetingSubscriber("Subscriber 2")
  val s3 = new GreetingSubscriber("Subscriber 3")
  Seq(s1, s2, s3).foreach(greeter.subscribe(_))

  greeter.greet("Hello world")