Type mismatch (String) using case class and actor

问题:

Some format issue when I'm trying to quote the code, so here is the picture :(

image description here

import akka.actor.{Actor, ActorSystem, Props}

case class Number(n: Int)
case class String(s: String)

class DoublingActor extends Actor {
  def receive: Receive = {
    case Number(n) => println(s"Result of doubling $n: ${n*2}")
    case String(s) => println(s"Result of doubling $s: ${s}${s}")
  }
}

object Double extends App {
  val system = ActorSystem("DoublerSystme")
  val doubler = system.actorOf(Props[DoublingActor], "doubler")

  doubler ! Number(5)
  doubler ! String("test")
}

The thing is, the actor works fine with number, but how can I add the matching function that returns the string twice?

回答1:

You should avoid naming your case class as String, especially in your case, with String parameter type:

case class String(s: String)

It would confuse the compiler to expect a parameter type different from the actual String type you want. Your app will work if you explicitly specify java.lang.String as the parameter type:

case class String(s: java.lang.String)

In any case, I would not recommend naming a case class as String.

回答2:

What behavior are you seeing? Due to your issue being wrapped in an image, I can't test for sure, but I'd expect that you are getting a compile error with the descriptive message object String is not a case class, nor does it have an unapply/unapplySeq member.

Because it doesn't have the unapply member, you'll need to modify your statement to

case s: String => println(s"Result of doubling $s: ${s}:${s}")