Using traits with a factory

Question

I'm currently discovering scala and I was wondering if I could use traits with a factory.

I tried this :

abstract class Foo {
  ...
}
object Foo {
  def apply() = new Bar

  private class Bar extends Foo {
    ...
  }
}

Foo() with MyTrait // Not working

I guess it's because with must be preceded by new.

So is there any way to do this ?

Thank you

Answer 1

No it is too late, the instance is already created when the apply() method returns.

What you can do is using the traits inside the factory method. The code below is from a rather big code example I am writing:

object Avatar {
 // Avatar factory method
 def apply(name: String, race: RaceType.Value, character: CharacterType.Value
  ): Avatar = {
    race match {
      case RaceType.Dwarf => {
        character match {
          case CharacterType.Thief => new Avatar(name) with Dwarf with Thief
          case CharacterType.Warrior => new Avatar(name) with Dwarf with Warrior
          case CharacterType.Wizard => new Avatar(name) with Dwarf with Wizard
        }
      }
      case RaceType.Elf => {
        character match {
          case CharacterType.Thief => new Avatar(name) with Elf with Thief
          case CharacterType.Warrior => new Avatar(name) with Elf with Warrior
          case CharacterType.Wizard => new Avatar(name) with Elf with Wizard
        }
      }
    }
  }
}

class Avatar(val name: String) extends Character {
  ...
}

In this code the type (profession and race) of your Avatar is decided in the factory based on the RaceType and CharacterType enumerations. What you have is one factory for all sorts of different types or type combinations.