Invalid covariant type with CRTP clonable class

Question

I\'m trying to implement a Clonable class with the CRTP. However, I need to have abstract class that have a pure virtual clone method, overridden by child classes. To make t

Answer 1

Even if B is indeed derived from Clonable, the problem here is that Clonable construction is not valid, as it defines

B* clone() const override

which of course is not an override of AbstractClonable::clone(), since the compiler doesn't see B at this point as a child of AbstractClonable. So I believe the issue lays in the fact that the compiler cannot build the Clonable base of B.

A workaround (but not really the same as what you want) is to define

Clonable* clone() const override

in Clonable. As you mentioned in the comment, you can also define a free function

template 
T* clone(const T* object) 
{ 
    return static_cast(object->clone()); 
}

Related: Derived curiously recurring templates and covariance