Method chaining + inheritance don't play well together?

Question

Consider:

// member data omitted for brevity

// assume that \"setAngle\" needs to be implemented separately
// in Label and Image, and that Button does need         


        

Answer 1

Not with C++.

C++ does not support variance in return types, so there's no way to change the static type of the reference returned from Widget.move() to be more specific than Widget& even if you override it.

The C++ needs to be able to check things at compile time, so you can't use the fact that what's really being returned from move is a button.

At best, you can do some runtime casting, but it's not going to look pretty. Just separate calls.

Edit: Yes, I'm well aware of the fact that the C++ standard says that return value covariance is legitimate. However, at the time I was teaching and practicing C++, some mainstream compilers (e.g., VC++) did not. Hence, for portability we recommended against it. It is possible that current compilers have no issue with that, finally.