template <class T = void> struct bit_not {
constexpr T operator()(const T& x) const;
};
constexpr T operator()(const T& x) const;
Returns: ~x.
template <> struct bit_not<void> {
template <class T> constexpr auto operator()(T&& t) const
-> decltype(~std::forward<T>(t));
using is_transparent = unspecified;
};
template <class T> constexpr auto operator()(T&&) const
-> decltype(~std::forward<T>(t));
Returns: ~std::forward<T>(t).