型リストから先頭N個の型を取り出すメタ関数です。
template <int N, class Seq> struct take; template <int N, class Head, class... Tail> struct take<N, tuple<Head, Tail...>> { typedef typename concat<tuple<Head>, typename take<N-1, tuple<Tail...>>::type >::type type; }; template <class Head, class... Tail> struct take<1, tuple<Head, Tail...>> { typedef tuple<Head> type; }; template <class Head, class... Tail> struct take<0, tuple<Head, Tail...>> { typedef tuple<> type; };
take<3, tuple<int, double, long, char, void*>>::type → tuple<int, double, long>
