[karmakaze]

Typescript seems to have no problem with it (nor do I suspect F#/OCaml):

  class A {
    x = 10;
    scale(n: number): void {
      this.x *= n;
    }
  }
  class B {
    y = 10;
    scale(n: number): void {
      this.y *= n;
    }
  }  
  var z: A | B;
  z = new A
  z.scale(2);
  z = new B
  z.scale(2);

I was also looking for Sum Types/anonymous enums[0].

[0] https://news.ycombinator.com/threads?id=karmakaze&next=33505...