template<int __i, int... _Indexes, typename _IdxHolder, typename...
_Elements>
struct __index_holder_impl<__i, __index_holder<_Indexes...>,
_IdxHolder, _Elements...>
{
typedef typename __index_holder_impl<__i + 1,
__index_holder<_Indexes...,
__i>,
_Elements...>::type type;
};
