250 struct nullopt_t  struct
253   constexpr explicit nullopt_t(init){}  in nullopt_t()  argument
255 constexpr nullopt_t nullopt{nullopt_t::init()};
353   static_assert( !std::is_same<typename std::decay<T>::type, nullopt_t>::value, "bad T" );
401   constexpr optional(nullopt_t) noexcept : OptionalBase<T>() {};  in optional()  argument
437   optional& operator=(nullopt_t) noexcept  in operator =()  argument
606   static_assert( !std::is_same<T, nullopt_t>::value, "bad T" );
615   constexpr optional(nullopt_t) noexcept : ref(nullptr) {}  in optional()  argument
630   optional& operator=(nullopt_t) noexcept {  in operator =()  argument
743 template <class T> constexpr bool operator==(const optional<T>& x, nullopt_t) noexcept  in operator ==()  argument
748 template <class T> constexpr bool operator==(nullopt_t, const optional<T>& x) noexcept  in operator ==()  argument
753 template <class T> constexpr bool operator!=(const optional<T>& x, nullopt_t) noexcept  in operator !=()  argument
758 template <class T> constexpr bool operator!=(nullopt_t, const optional<T>& x) noexcept  in operator !=()  argument
763 template <class T> constexpr bool operator<(const optional<T>&, nullopt_t) noexcept  in operator <()  argument
768 template <class T> constexpr bool operator<(nullopt_t, const optional<T>& x) noexcept  in operator <()  argument
773 template <class T> constexpr bool operator<=(const optional<T>& x, nullopt_t) noexcept  in operator <=()  argument
778 template <class T> constexpr bool operator<=(nullopt_t, const optional<T>&) noexcept  in operator <=()  argument
783 template <class T> constexpr bool operator>(const optional<T>& x, nullopt_t) noexcept  in operator >()  argument
788 template <class T> constexpr bool operator>(nullopt_t, const optional<T>&) noexcept  in operator >()  argument
793 template <class T> constexpr bool operator>=(const optional<T>&, nullopt_t) noexcept  in operator >=()  argument
798 template <class T> constexpr bool operator>=(nullopt_t, const optional<T>& x) noexcept  in operator >=()  argument