Scala pattern matching confusion with Option[Any]

Question

I have the following Scala code.

import scala.actors.Actor

object Alice extends Actor {
  this.start
  def act{
    loop{
      react {
        case \"Hello\" =         


        

Answer 1

This is due to type-erasure. The JVM does not know of any type parameter, except on arrays. Because of that, Scala code can't check whether an Option is an Option[Int] or an Option[String] -- that information has been erased.

You could fix your code this way, though:

object Test {
  def test = {
    (Alice !? (100, "Hello")) match {
      case Some(i: Int) => println ("Int received "+i)
      case Some(s: String) => println ("String received "+s)
      case _ =>
    }
    (Alice !? (100, 1)) match {
      case Some(i: Int) => println ("Int received "+i)
      case Some(s: String) => println ("String received "+s)
      case _ =>
    }
  }
}

This way you are not testing what the type of Option is, but what the type of its contents are -- assuming there is any content. A None will fall through to the default case.