Is it possible to define an implementation template specialization as typedef of another type?

Question

I have a class template for which I want to introduce several template specializations. Those template specializations identical to some existing type. Conceptually I would

Answer 1

Assuming only certain specialisations of Common are aliases of TypeZ then you can do:

template class Common {
    struct type {
        /// general implementation
    };
};

template<> class Common { using type = TypeZ; };
template<> class Common { using type = TypeZ; };
template<> class Common { using type = TypeZ; };

template using common_t = typename Common::type;

Then you use common_t rather than Common.

Just to entertain the inheritance idea, have you tried this?

template<> class Common : public TypeZ { using TypeZ::TypeZ; };
template<> class Common : public TypeZ { using TypeZ::TypeZ; };
template<> class Common : public TypeZ { using TypeZ::TypeZ; };

Then you don't need to use a nested type alias.