Question

When I need to pass typed collections to an actor, I get an “unchecked” warning in my react method:

val actor = actor {
  loop {
    react {
      case a:List[String] => // do something
    }
  }
}

How can I work around this? I tried boxing collection in a separate class (but that is ugly and cumbersome), and just casting collection (case a:List[_] => a.asInstanceOf[List[String]]) after receiving it by actor is not type-safe and dangerous.

Answer 1

Because the JVM does not keep track of the type of generics, you can’t know that a List[_] is a List[String] unless you examine every element and check that it is a string. Your best bet is in fact to box the collection in a separate class. It need not be so bad!

case class StringsBox(ls: List[String]) {}

//...
myactor ! StringsBox( List("these","are","strings") )

//...
react {
  case StringsBox(ls) =>  /* Now you have your List[String] */
}