How to extend case class with type parameter?

Question

I have the following case class that I would like to extend:

case class Message[A](ackTo: ActorRef[Ack], msg: A)

I've tried:

case class KafkaMessage() extends Message[KafkaHealthEvent]
    with ServerHealthStreamer

case class SapMessage() extends Message[SapHealthEvent]
    with ServerHealthStreamer

But I do not know, how to extend it correctly. The whole type definition:

object ServerStreamer {

  sealed trait Ack

  object Ack extends Ack

  sealed trait ServerHealthStreamer

  case class Message[A](ackTo: ActorRef[Ack], msg: A)

  case class Init(ackTo: ActorRef[Ack]) extends ServerHealthStreamer

  case class KafkaMessage() extends Message[KafkaHealthEvent]
    with ServerHealthStreamer

  case class SapMessage() extends Message[SapHealthEvent]
    with ServerHealthStreamer

  case object Complete extends ServerHealthStreamer

  case class Fail(ex: Throwable) extends ServerHealthStreamer

}

How to extend it correctly?

You don't mention it, but I assume you're getting an error because you can't extend a case class and make another case class with it? Anyway, since you seem to be streaming, why not use akka streams directly? — Reactormonk
– Reactormonk, Commented Jul 14, 2019 at 17:50
case class is not used for inheritance or implementing traits — SwiftMango
– SwiftMango, Commented Jul 14, 2019 at 17:50

Tim · Accepted Answer · 2019-07-14 18:08:57Z

3

As explained in the comments, you can't extend a case class. So just make Message a normal class or trait

answered Jul 14, 2019 at 18:08

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Tim

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Comments

Daniel · Accepted Answer · 2021-08-06 19:44:02Z

0

You can extend a case class but the extended object cannot be a case class itself, only a class. Additionally, note that the case class which is being extended must have its properties initialised in the extending class' construction:

// Let KafkaActorRef extend ActorRef[Ack]
class KafkaMessage(kafkaActorRef: KafkaActorRef) extends Message[KafkaHealthEvent](kafkaActorRef, "someMessage")

Here you can see that the values of the extended case class are assigned in the class construction.

answered Aug 6, 2021 at 19:44

Daniel

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