20 General utilities library [utilities]

20.6 Optional objects [optional]

template<class T, class U> constexpr bool operator==(const optional<T>& x, const U& v);

Mandates: The expression *x == v is well-formed and its result is convertible to bool.

[Note 1:

T need not be Cpp17EqualityComparable.

— end note]

Effects: Equivalent to: return bool(x) ? *x == v : false;

template<class T, class U> constexpr bool operator==(const T& v, const optional<U>& x);

Mandates: The expression v == *x is well-formed and its result is convertible to bool.

Effects: Equivalent to: return bool(x) ? v == *x : false;

template<class T, class U> constexpr bool operator!=(const optional<T>& x, const U& v);

Mandates: The expression *x != v is well-formed and its result is convertible to bool.

Effects: Equivalent to: return bool(x) ? *x != v : true;

template<class T, class U> constexpr bool operator!=(const T& v, const optional<U>& x);

Mandates: The expression v != *x is well-formed and its result is convertible to bool.

Effects: Equivalent to: return bool(x) ? v != *x : true;

template<class T, class U> constexpr bool operator<(const optional<T>& x, const U& v);

Mandates: The expression *x < v is well-formed and its result is convertible to bool.

Effects: Equivalent to: return bool(x) ? *x < v : true;

template<class T, class U> constexpr bool operator<(const T& v, const optional<U>& x);

Mandates: The expression v < *x is well-formed and its result is convertible to bool.

Effects: Equivalent to: return bool(x) ? v < *x : false;

template<class T, class U> constexpr bool operator>(const optional<T>& x, const U& v);

Mandates: The expression *x > v is well-formed and its result is convertible to bool.

Effects: Equivalent to: return bool(x) ? *x > v : false;

template<class T, class U> constexpr bool operator>(const T& v, const optional<U>& x);

Mandates: The expression v > *x is well-formed and its result is convertible to bool.

Effects: Equivalent to: return bool(x) ? v > *x : true;

template<class T, class U> constexpr bool operator<=(const optional<T>& x, const U& v);

Mandates: The expression *x <= v is well-formed and its result is convertible to bool.

Effects: Equivalent to: return bool(x) ? *x <= v : true;

template<class T, class U> constexpr bool operator<=(const T& v, const optional<U>& x);

Mandates: The expression v <= *x is well-formed and its result is convertible to bool.

Effects: Equivalent to: return bool(x) ? v <= *x : false;

template<class T, class U> constexpr bool operator>=(const optional<T>& x, const U& v);

Mandates: The expression *x >= v is well-formed and its result is convertible to bool.

Effects: Equivalent to: return bool(x) ? *x >= v : false;

template<class T, class U> constexpr bool operator>=(const T& v, const optional<U>& x);

Mandates: The expression v >= *x is well-formed and its result is convertible to bool.

Effects: Equivalent to: return bool(x) ? v >= *x : true;

template<class T, three_way_comparable_with<T> U>
  constexpr compare_three_way_result_t<T,U>
    operator<=>(const optional<T>& x, const U& v);

Effects: Equivalent to: return bool(x) ? *x <=> v : strong_ordering::less;