Using variadic template as parameter for both class and method

Question

My question is about the following piece of code:

    template <class...T>
    class A
    {
    public:
        template <class...S>
        static void a() { }
    };

    template <class...T>
    class B
    {
    public:
        template <class...S>
        void b()
        {
            A<T...>::a<S...>();
        }
    };

    int main(int argc, char** argv)
    {
        return 0;
    }

I have a class A that has a variadic template and contains a static method a that has another variadic template. From somewhere else (class B in this case) I have two different sets of variadic templates I want to pass to A::a.

The compiler (GCC 4.8.1) gives the following error message:

    main.cpp: In static member function ‘static void B<T>::b()’:
    main.cpp:16:22: error: expected primary-expression before ‘...’ token
             A <T...>::a<S...>();
                          ^
    main.cpp:16:22: error: expected ‘;’ before ‘...’ token

Also notice that when I change the method b() to this:

        void b()
        {
            A<int, char, short>::a<S...>();
        }

or some other specification of A's templates then the code compiles just fine.

What is wrong with the above code?

Answer 1

add template here

A<T...>::template a<S...>();

see comment for reason. Also this compile nicely on VC++ without the keyword so I guess it is compiler dependent.