#if defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) < 407) # define OLD_GNU #endif #ifdef OLD_GNU template <int... Is> struct Interface; #endif template <int I, int... Is> struct Interface #ifdef OLD_GNU <I, Is...> #endif { static int accumulate() { return I + Interface<Is...>::accumulate(); } }; template <int I> struct Interface<I> { static int accumulate() { return I; } }; // Note: split this into a separate test if a // cxx_variadic_template_template_parameters feature is added. template <typename T> struct eval { enum { Matched = 0 }; }; template <template <typename...> class T, typename... U> struct eval<T<U...>> { enum { Matched = 1 }; }; template <typename...> struct A { }; template <typename T> struct B { }; template <typename T, typename U> struct C { }; template <typename T, typename U, typename...> struct D { }; // Note: This test assumes that a compiler supporting this feature // supports static_assert. Add a workaround if that does not hold. static_assert(eval<A<>>::Matched, "A Matches"); static_assert(eval<A<int>>::Matched, "A Matches"); static_assert(eval<A<int, char>>::Matched, "A Matches"); static_assert(eval<B<int>>::Matched, "B Matches"); static_assert(eval<C<int, char>>::Matched, "C Matches"); static_assert(eval<D<int, char>>::Matched, "D Matches"); static_assert(eval<D<int, char, bool>>::Matched, "D Matches"); static_assert(eval<D<int, char, bool, double>>::Matched, "D Matches");