scala generic method overriding

Question

I have an abstract class :

abstract class Foo(...){
   def bar1(f : Foo) : Boolean
   def bar2(f : Foo) : Foo
}

multiple classes extend Foo and override the methods

class FooImpl(...) extends Foo{
    override def bar1(f : Foo) : Boolean {
        ...
    }
    override def bar2(f : Foo) : Foo {
        ...
    }
} 

Is it possible, using generics (or something) to make the overriding methods have the parametertype of the subclass implementing it? Like this :

class FooImpl(...) extends Foo{
    override def bar1(f : FooImpl) : Boolean {
        ...
    }
    override def bar2(f : FooImpl) : FooImpl {
        ...
    }
}

I was thinking something along the line of the following, but that didn't seem to work...

abstract class Foo(...){
    def bar1[T <: Foo](f : T) : Boolean
    def bar2[T <: Foo](f : T) : T
}

class FooImpl(...) extends Foo{
    override def bar1[FooImpl](f : FooImpl) : Boolean {
       ...
    }
    override def bar2[FooImpl](f : FooImpl) : FooImpl{
       ...
    }
}

Any help is much appreciated!

Thank you.

Answer 1

abstract class Foo{
   type T <: Foo
   def bar1(f:T):Boolean
   def bar2(f:T):T
}

class FooImpl extends Foo{
   type T = FooImpl
   override def bar1(f:FooImpl) = true
   override def bar2(f:FooImpl) = f
}

In this version, different subclasses of Foo all share Foo as a superclass, but to hold the return value of bar2 (or the parameters to bar1 or bar2) in a setting where all you know about your object (let's say it's named obj) is that it's a Foo, you need to use the type obj.T as the type of the variable.