Call superclass apply method in scala

Question

trait A {
    def a
    def b
    def c
}

object A {
    def apply = {
        new A {
            def a = 1
            def b = 2
            def c = 3
        }
    }
}

See i have a trait A here and the companion object's apply method implements it.

trait B extends A {
    def d
}

object B {
    def apply = {
        new B {
            def d = 4
        }
    }
}

Trait B of course won't compile since I have to also implement A's a/b/c methods, but is there a way I can call A's apply method and then just implement B's d method?

I think to override a/b/c in B.apply and just call super.a/b/c is one way, but what if it has multiple layers A->B->C->D, I don't want to override all superclass's method in the leaf node.

Any thoughts would help, thanks!

Answer 1

If you can change A, I think the most reasonable solution is to give a name to the anonymous class returned from A.apply():

object A {
    class AImpl extends A {
        def a = 1
        def b = 2
        def c = 3
    }
    def apply = new AImpl
}

object B {
    def apply = {
        new AImpl with B {
            def d = 4
        }
    }
}

I think to override a/b/c in B.apply and just call super.a/b/c is one way

No, that won't work. If it did, there would be no need to override them.