How to receive Generic Event in Actor

Question

I tried to write a generic Actor and it can receive generic event

case class CreateEvent[T](t: T)

trait MyBaseActor[Type] extends Actor {
    override def receive: Receive = {
      case CreateEvent(t: Type) => ....
    }
}

Then, I create an real actor

case class HasName(name: String)

class MyActor extends MyBaseActor[HasName]

And I expect MyActor can handle message Create(HasName("hello") as well. But when I compile code, I got this warning:

abstract type pattern Type is unchecked since it is eliminated by erasure

And my actor can't receive CreateEvent also. Maybe I don't understand enough about Generic in scala, please help me explain why it not work and how can I fix it

Type here is just Generic type, I don't have any trait or class for it — khacsinhcs, Jan 22 '19 at 08:07
create type name Type and use it like this or you can create empty trait or case object. — Raman Mishra, Jan 22 '19 at 08:10
In your case I´d suggest taking a look to Akka Typed: https://doc.akka.io/docs/akka/2.5/typed/index.html — Emiliano Martinez, Jan 22 '19 at 08:34
I suggest you read about type erasure in Scala, you may find some solutions for your case here: https://stackoverflow.com/questions/1094173/how-do-i-get-around-type-erasure-on-scala-or-why-cant-i-get-the-type-paramete — mkUltra, Jan 22 '19 at 09:37

Aleksey Isachenkov · Accepted Answer · 2019-01-22T10:41:08.713

It does not work because of type erasure. In runtime, any instance of CreateEvent has type CreateEvent[Object] so you can't match its generic type.

To work around it you can use ClassTag:

trait MyBaseActor[Type] extends Actor {
  val classTag: ClassTag[Type]

  override def receive: Receive = {
    case CreateEvent(t) if classTag.runtimeClass.isInstance(t) =>
      val typedT: Type = t.asInstanceOf[Type]
      ....
  }
}
class MyActor() extends MyBaseActor[HasName] {
  override final val classTag: ClassTag[HasName] = implicitly[ClassTag[HasName]]
}

How to receive Generic Event in Actor

1 Answers1