Is there something like Map.keySet for a partial function in scala?

Question

More specifically, I have:

case class Key (key: String)
abstract class abstr {
  type MethodMap = PartialFunction[Key,  String => Unit]
  def myMap: MethodMap // abstract

  def useIt (key: Key, value: String) = {
    val meth = myMap(key)
    meth(value)
  }

  def report = {
    for (key <- myMap.keySet) // how to do this
      println("I support "+key)
  }
}

I use it like this:

class concrete extends abstr {
  var one: Boolean
  def method1(v: String): Unit = ???
  def method2(v: String): Unit = ???

  def map1: MethodMap = {
    case Key("AAA") => method1
  }
  def map2: MethodMap = {
    case Key("AAA") => method2
  }

  override def myMap: MethodMap = if (one) map1 else map2
}

Of course, this is somewhat simplified, but the report function is necessary.

Some history: I first had it implemented using Map but then I changed it to PartialFunction in order to support the following override def myMap: MethodMap = if (one) map1 else map2 .

Any suggestion to refactor my code to support everything is also appreciated.

Answer 1

No. PartialFunction can be defined (and often is) on infinite sets. Eg what do you expect report to return in these situations:

class concrete2 extends abstr {
  def myMap = { case Key(_) => ??? }
}

or

class concrete2 extends abstr {
  def myMap = { case Key(key) if key.length > 3 => ??? }
}

? If you have a finite list of values you are interested in, you can do

abstract class abstr {
  type MethodMap = PartialFunction[Key,  String => Unit]
  def myMap: MethodMap // abstract
  val keys: Seq[Key] = ...

  def report = {
    for (key <- keys if myMap.isDefined(key))
      println("I support "+key)
  }
}

Some history: I first had it implemented using Map but then I changed it to PartialFunction in order to support the last line in second part.

Why? This would work just as well with Map .

In your solution, is there any way to define the domain of the partial function to be the finite set keys

def f: MethodMap = { case key if keys.contains(key) => ... }

Of course, the domain isn't part of the type.