Using template base class template constructor in derived class

Question

i know that you can use constructors from a base class in a derived class like

class A {
public:
    A() {};
}

class B : public A {
public:
    using A::A;
}

Furthermore you can use a constructor from a template base class like

template<typename T>
class A {
public:
    A() {};
}

template<typename T>
class B : public A<T> {
public:
    using A<T>::A;
}

Suppose that class A now has a template function as constructor:

template<typename T1>
class A {
public:
    template<typename T2>
    A() {};
}

template<typename T1>
class B : public A<T1> {
public:
    using A<T1>::A;                           // nope
    using A<T1>::A<>;                         // neither             
    template<typename T2> using A<T1>::A<T2>; // sounds good, doesn't work

}

How could you use the base class constructor in the derived class?

Answer 1

Two things:

• template<typename T2> A() {} is unusuable as a constructor, since there is no way to deduce T2 .
• You can only inherit all constructors at once. You can't choose specific ones.

Other than that, using A<T1>::A; is correct.