In scala multiple inheritance, how to resolve conflicting methods with same signature but different return type?

Question

Consider the code below:

trait A {
  def work = { \"x\" }
}

trait B {
  def work = { 1 }
}

class C extends A with B {
  override def work = super[A].work
}         


        

Answer 1

You can't do that.

Look at this piece of code:

val c = new C
val a: A = c
val b: B = c

There is no way that both of these lines could work:

val s: String = a.work
val i: Int = b.work

If we allowed such code to compile, one of these assignments would have to throw a ClassCastException or fail in another way. So, it simply isn't possible to resolve such conflict.

I guess you have to workaround this with some form of delegation, maybe something like this:

class C extends A {
  def toB = new B {
    //implement B methods by somehow delegating them to C instance
  }
}