tuple 구현

#include <iostream>
#include <type_traits>
#include <typeinfo>
using namespace std;
template<typename … Types>
struct xtuple
{
    static constexpr int Size = 0;
};

template<typename T, typename … Types>
struct xtuple<T, Types …> : xtuple<Types …>
{
    T value;
    static constexpr int Size = xtuple<Types …>::Size + 1;
    xtuple() = default;
    xtuple(const T& t, Types … args) : value(t), xtuple<Types …>(args …) {}
};

template<int N, typename T> struct xtuple_get
{
};

template<typename T, typename … Types>
struct xtuple_get<0, xtuple<T, Types …>>
{
    using VT = T;
    using TT = xtuple<T, Types …>;
};

template<int N, typename T, typename … Types>
struct xtuple_get<N, xtuple<T, Types …>>
{
    using VT = typename xtuple_get<N – 1, xtuple<Types …>>::VT;
    using TT = typename xtuple_get<N – 1, xtuple<Types …>>::TT;
};

template<int N, typename T, typename … Types>
typename xtuple_get<N, xtuple<T, Types …>>::VT xget(xtuple<T, Types …>& xt)
{
    using TT = typename xtuple_get<N, xtuple<T, Types …>>::TT;
    return static_cast<TT&>(xt).value;
}

int main()
{
    int v0 = 10101;
    xtuple<int> a(1);
    xtuple<int, short, double> b(v0,2,3.4);
    cout << xget<0>(b) << endl;
    cout << xget<1>(b) << endl;
    cout << xget<2>(b) << endl;
}