CODEWITHSUNDEEP
scalapartialfunction
fmpwizard
fmpwizard

Reputation: 2768

Partial Function pattern match split into a class and a trait

Lift uses a PartialFunction on their implementation of Comet Actors, and you usually end up with this on your class:

override def lowPriority: PartialFunction[Any,Unit] = {
  case MyCaseClass1(a)        => do something here
  case MyCaseClass2(a)        => do something here
  case AlwaysPresentCaseClass => default action
}

What I'd like to do, and I'm not sure if it is even possible is to split that Partial Function so that the last case can be moved into a trait.

So when I have a new comet actor I simply do:

class MyNewComet extends MyActorTrait {
  override def lowPriority: PartialFunction[Any,Unit] = {
    case MyCaseClass1(a)        => do something here
    case MyCaseClass2(a)        => do something here
  }
}

And Somehow the trait MyActorTrait will have the missing

case AlwaysPresentCaseClass => default action

Upvotes: 1

Views: 1389

Answers (2)

0__
0__

Reputation: 67280

You can compose partial functions using the orElse method:

val f1: PartialFunction[Any, String] = {
  case 22 => "hallo"
}
val f2: PartialFunction[Any, String] = {
  case "rara" => "welt"
}

val f = f1 orElse f2 // f falls back to f2 if undefined in f1
f(22)
f("rara")

Upvotes: 9

Daniel C. Sobral
Daniel C. Sobral

Reputation: 297155

Try this:

trait MyActorTrait extends /* whatever class provides lowPriority */ {
   def default: PartialFunction[Any, Unit] = {
           case AlwaysPresentCaseClass => default action
   }

   abstract override def lowPriority: PartialFunction[Any,Unit] =
       super.lowPriority orElse default
}

The only problem is that you can't do MyNewComet extends MyActorTrait. Instead, you can either have class MyNewCometDefault extends MyNewComet with MyActorTrait, or new MyNewComet with MyActorTrait.

Upvotes: 0

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