template <class T, T v> struct integral_constant { static constexpr T value = v; typedef T value_type; typedef integral_constant type; // using injected-class-name constexpr operator value_type() const noexcept { return value; } }; using false_type = integral_constant<bool, false>; using true_type = integral_constant<bool, true>; template <class T, class U> struct is_same : false_type {}; template <class T> struct is_same<T, T> : true_type {};