override function in trait

Question

Let's say I have the following trait

trait Foo[T] {
  def overrideMe(other:Foo[T]) : Int
}

I would like to be able to do

class Bar extends Foo[Int] {
   override  def overrideMe(other:Bar) : Int = other.BarFn
}

but it does not compile. The reason is that I would like overrideMe to be able to use functionality of the subtype. I could do something like

class Bar extends Foo[Int] {
   override  def overrideMe(other:Foo[Int]) : Int = {
      other.asInstanceOf[Bar].BarFn
}

but that doesn't look very nice.

Is it possible to say in the trait that the virtual funcation can be overridden with a subtype?

edit @agilesteel That almost works, but I run into trouble if I have a function in another class relying only on the trait Foo

class Test[T] {
    def callOverrideMe(a : Foo[T], b : Foo[T] ) : Int = a.overrideMe(b)
}

I get a compile error: type mismatch; found b.type (with underlying type foo.Foo[T]) required a.SubType

Answer 1

trait Foo[T] {
  type TheSubType <: Foo[T]
  def overrideMe(other: TheSubType) : Int
}

class Bar extends Foo[Int] {
   type TheSubType = Bar
   override def overrideMe(other: Bar) : Int = other.barFn
   def barFn = 10
}