overriding virtual function return type differs and is not covariant

Question

Ah, SO came back just in time.

I am getting a strange error:

 \'B::blah\': overriding virtual function return type differs and is not covariant from          


        

Answer 1

Imagine that your example worked.

Consider the following code:

A *a = some_function();
A::Inner inner = a->blah();

If the dynamic type of a is B*, then a->blah() calls a::B->blah(), and returns a B::Inner. This is then silently sliced into an instance of A::Inner. In general, this (and any type of slicing) is not what you want. I find this to be a good restriction.