Scala: How to extend an Akka actor? - scala

Question

I wrote an Akka base-actor that can handle some common messages. I want to reuse this basic behavior in a sub-actor, by extending the base-actor (not by composition of the base-actor).
I have seen several approaches in previous questions. They are all valid but also may be improved:
How extend behaviour of super actor in akka
and
How do I best share behavior among Akka actors?
To make the implementation cleaner, I am trying to achieve the following:
When defining the sub-actor, I try to extend only the base-actor (not both Actor and sub-actor). However, I was not able to force the compiler to do this.
I also try to not rename the receive partial function, because it is a kind of convention.
Here is a sample of my implementation:
//This is the base-actor that implements the common behavior
trait BetterActor extends Actor {
abstract override def receive = {
super.receive orElse { case _ => println("Missing pattern!") }
}
}
//This is the actor that implements the additional behavior.
//I actually wanted to extend BetterActor. It was not possible.
class MyActor extends Actor {
def receive = {
case i: Int =>
println(s"Yay!!! Got $i")
}
}
Here are two alternative ways how I can create an instance of the sub-actor, which combines both the common and the additional behaviors:
//1.
val myBetterActor = system.actorOf(Props(new MyActor with BetterActor), "myBetterActor")
//2.
class MyBetterActor extends MyActor with BetterActor
val myBetterActor = system.actorOf(Props[MyBetterActor], "myBetterActor")
Finally, I may invoke the sub-actor by:
myBetterActor ! 2
myBetterActor ! "a"
Problems with my implementation:
When I create an instance of the sub-actor, only then I can mix in the base-actor, either directly (1) or by defining a new class that mixes in the base-actor.
Like I said before, I would prefer to mix in the base-actor when I define the sub-actor. Not when I try to create an instance of the sub-actor.
P.S. It's fascinating that the designers of this framework did not see it necessary to make this common requirement easy to accomplish.

Answer 1

i suppose as long as you're not trying to override behavior with BetterActor, you could try something like this:
trait BetterActor extends Actor {
override def unhandled(message: Any): Unit = message match {
case e: CommonMessage => println("COMMON!")
case e => super.unhandled(e)
}
}
class MyActor extends BetterActor {
override def receive = {
case i: Int => println(s"Yay!!! Got $i")
}
}