gistfile1.cpp

#include <cstddef>

template<class T, T... I>
struct integer_sequence {
    using value_type = T;
    static constexpr std::size_t size() noexcept { return sizeof...(I); }
};

namespace detail {    
    template<class, class> struct Combine;
    template<class T, T ...I, T ...J>
    struct Combine<integer_sequence<T, I...>, integer_sequence<T, J...>> {
        using type = integer_sequence<T, I..., (sizeof...(I) + J)...>;
    };
    
    template<class T, T N, int = (N == 0 || N == 1) ? N : 2>
    struct Seq {
        static_assert(N >= 0, "N must be nonnegative in make_integer_sequence<T, N>");
        using type = typename Combine<typename Seq<T,     N/2>::type,
                                      typename Seq<T, N - N/2>::type>::type;
    };
    
    template<class T, T N> struct Seq<T, N, 0> { using type = integer_sequence<T>; };
    template<class T, T N> struct Seq<T, N, 1> { using type = integer_sequence<T, 0>; };
};

template<class T, T N> using make_integer_sequence = typename detail::Seq<T, N>::type;
template<std::size_t... I> using index_sequence = integer_sequence<std::size_t, I...>;
template<std::size_t N> using make_index_sequence = make_integer_sequence<std::size_t, N>;
template<class... T> using index_sequence_for = make_index_sequence<sizeof...(T)>;