Integer_sequence - C++ - Ответ 6381162

#include <iostream>
#include <array>
#include <utility>
#include <tuple>
 
namespace isq {
 
template< class T, T... Ints >
class integer_sequence {
   static size_t size() { return sizeof...(Ints); }
};
 
template<std::size_t... Ints>
using index_sequence = integer_sequence<std::size_t, Ints...>;
 
template<class T, T... N>
using make_integer_sequence = integer_sequence<T, N... >;
 
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)>;
 
} //namespace isq
 
//////////////////////////////////////////////////////////////////////////////////////////
 
/// // Convert array into to tuple
template<typename Array, std::size_t... I>
auto a2t_impl(const Array& a, isq::index_sequence<I...>)
-> decltype(std::make_tuple(a[I]...))
{
   return std::make_tuple(a[I]...);
}
 
template<typename T, std::size_t N, typename Indices = isq::make_index_sequence<N>>
auto a2t(const std::array<T, N>& a)
-> decltype(a2t_impl(a, Indices()))
{
   return a2t_impl(a, Indices());
}
 
template<class Ch, class Tr, class Tuple, std::size_t... Is>
void print_tuple_impl(std::basic_ostream<Ch,Tr>& os,
                      const Tuple & t,
                      isq::index_sequence<Is...>)
{
   using swallow = int[];
   (void)swallow{0, (void(os << (Is == 0? "" : ", ") << std::get<Is>(t)), 0)...};
}
 
template<class Ch, class Tr, class... Args>
auto operator<<(std::basic_ostream<Ch, Tr>& os, const std::tuple<Args...>& t)
-> std::basic_ostream<Ch, Tr>&
{
   os << "(";
   print_tuple_impl(os, t, isq::index_sequence_for<Args...>{});
   return os << ")";
}
 
int main()
{
   std::array<int, 4> array = {1,2,3,4};
 
   // convert an array into a tuple
   auto tuple = a2t(array);
   static_assert(std::is_same<decltype(tuple),
                 std::tuple<int, int, int, int>>::value, "");
 
   // print it to cout
   std::cout << tuple << '\n';
 
   system("pause");
   return 0;
}