For example
GeneralType is a class or a trait extended by many more specific types, including, to say, SpecificType.
A function takes an argument of type GeneralType, and then whant's no know if the actual argument passed is a SpecificType instance and act accordingly (use its special fields/methods) if it is.
How to code this in Scala 2.8?
In a word... "Pattern Matching":
def method(v : Vehicle) = v match {
case l : Lorry => l.deliverGoods()
case c : Car => c.openSunRoof()
case m : Motorbike => m.overtakeTrafficJam()
case b : Bike => b.ringBell()
case _ => error("don't know what to do with this type of vehicle: " + v)
}
Put this script in a file:
trait GeneralType
class SpecificType extends GeneralType
def foo(gt: GeneralType) {
gt match {
case s: SpecificType => println("SpecificT")
case g: GeneralType => println("GeneralT")
}
}
val bar = new AnyRef with GeneralType
val baz = new SpecificType()
foo(bar)
foo(baz)
Run the script:
scala match_type.scala
GeneralT
SpecificT
