integer sequence c++ 11

seq.hh

//copied from http://stackoverflow.com/questions/17424477/implementation-c14-make-integer-sequence

template<int...> struct seq { using type = seq; };
template<typename T1, typename T2> struct concat;
template<int... I1, int... I2> struct concat<seq<I1...>, seq<I2...>>: seq<I1..., (sizeof...(I1) + I2)...> {};

template<int N> struct gen_seq;
template<int N> struct gen_seq: concat<typename gen_seq<N/2>::type, typename gen_seq<N-N/2>::type>::type {};
template <> struct gen_seq<0>: seq<>{};
template <> struct gen_seq<1>: seq<0>{};

//sample
template<int N> struct fab { const static long n = fab<N-1>::n + fab<N-2>::n; };
template <> struct fab<0> { const static long n = 0; };
template <> struct fab<1> { const static long n = 1; };
template <> struct fab<2> { const static long n = 1; };

#include <vector>
template<int... Is> std::vector<long> vseq(const seq<Is...>&) { return std::vector<long>{fab<Is>::n...}; }
template<int N> std::vector<long> vseq() { return vseq(gen_seq<N>()); }