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

Following trick requires GNU g++, with C++14.

If some_constraints and different_constraints are mutually exclusive, you can add using base::operator auto; in derived class to make all the conversion operators of base available.

Example:

struct Base {
protected:
    // conversion to pointer types (protected).
    template::value>::type>
    operator T() const;
};

struct Derived : public Base{
    // Make all Base conversion operators public.
    using Base::operator auto;

    // conversion to default constructible & non-pointer types.
    // added an extra typename=void to distinguish from Base template operator.
    template::value>::type,typename=void>
    operator T() const;
};

Live demo