路径依赖类型和泛型

Question

I am looking at an example from Abstract Members . We have the following example of path-dependent types.

class Food

abstract class Animal {
  type SuitableFood <: Food

  def eat(food: SuitableFood): String
}

class DogFood extends Food

class Dog extends Animal {
  type SuitableFood = DogFood

  override def eat(food: DogFood): String = food.toString
}

val lassie = new Dog
lassie eat new lassie.SuitableFood

Say we want to work with eat in an class in the following manner

class D[T <: Animal] {
  def blah(t: T, p: T): String = {
    t.eat(t)
  }
}

I get type mismatch; expected t.SuitableFood, actual: T type mismatch; expected t.SuitableFood, actual: T . I see that I am entering the waters of generics and path-dependent types. I'd appreciate any help.

Thanks

Answer 1

How do I say it's of type SuitableFood?

def blah(t: T)(food: t.SuitableFood) = ...

Note that it has to be in a separate parameter list to depend on t .

The reason def blah(t: T, food: T#SuitableFood) doesn't work is because it would allow below code:

val lassie: Animal = new Dog
val cat: Animal = new Cat
val catFood: Animal#SuitableFood = new cat.SuitableFood
blah(lassie, catFood)