20 General utilities library [utilities]

20.6 Optional objects [optional]

20.6.7 Comparison with nullopt [optional.nullops]

template<class T> constexpr bool operator==(const optional<T>& x, nullopt_t) noexcept;
Returns: !x.
template<class T> constexpr strong_ordering operator<=>(const optional<T>& x, nullopt_t) noexcept;
Returns: x.has_­value() <=> false.