If C# used return type in method signatures

abstract class C {
  abstract C SomeOp();
}

class A : C {
  C SomeOp() {
    return SomeOp() as A;
  }

  A SomeOp() {
    return this;
  }
}

class B : C {
  C SomeOp() {
    return SomeOp() as B;
  }

  B SomeOp() {
    return this;
  }
}

class Foo {
  void Bar() {
    A a = new A();
    B b = new B();
    A otherA = a.SomeOp(); // no cast needed type inferred
    B otherB = b.SomeOp(); // no cast needed type inferred
    C c = a.SomeOp(); // no cast needed, type inferred
    c.SomeOp(); // not ambiguous, only one method with this name
    a.SomeOp() as A; // ambigous without assignment
  }
}