How to get the domain of a Partial Function in Scala?

Question

Is it possible to get the domain of a Partial Function in Scala?

Ex:

    val f: PartialFunction[Int, Unit] = {

      case 1 => println("This is 1")

      case 2 => println("This is 2")

   }

Is there any way to get something like:

    val list = f.getDomain

which would indicate values 1 and 2?

Update: I am trying to build an notification system (event bus). The subscriber will look like this:

    class SomeSubscriber extends Subscriber {

    notifications {

      case LoginEvent(date) => println("Login on " + date)

      case LogoutEvent(date) => println("Logout on " + date)

      case e: Notification[Any] => async {

         println("Other notification: " + e)

         ui {

          println("UI in async! " + e)

         }

       }

     }

   }

In my NotiticationService (the event dispatcher) I want to access the events declared in every 'notifications' block so I can push the notifications to the subscribers. How can I do that?

Thanks in advance.

Answer 1

If you have a collection, and you'd like to know which elements also belong to the domain of f, you can use filter and isDefinedAt like so:

scala> 1 to 10 filter f.isDefinedAt
res1: scala.collection.immutable.IndexedSeq[Int] = Vector(1, 2)

This simply checks exhaustively. I don't know if there is any better way.

Answer 2

It's inherently impossible, since a partial function may be defined for any subset of the input range; the input range itself may not be finite, in which case the domain would not necessarily be finite either. You can only obtain the domain via an exhaustive match (per Dan's answer), however you cannot exhaustively search an infinite input space.