Bring templated base class conversion operator into derived scope

Question

I have a base class that defines a constrained templated conversion operator

struct base {
    template 

        

Answer 1

To achieve a similar effect, you could move the constraints inside the operator and call the base conversion operator if the constraints are not satisfied:

struct base {
    template , int> = 0>
    operator C() const;
};

struct derived : base {
    template 
    operator P() const {
        if constexpr (different_constraints
) {
            // Overridden operator
        } else {
            return base::operator P();
        }
    }
};

Or equivalently have one regular std::enable_if_t, int> = 0 conversion operator and another std::enable_if_t, int> = 0 that calls the base conversion operator.