22 General utilities library [utilities]

22.5 Optional objects [optional]

22.5.6 Relational operators [optional.relops]

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template<class T, class U> constexpr bool operator==(const optional<T>& x, const optional<U>& y);
1
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Mandates: The expression *x == *y is well-formed and its result is convertible to bool.
[Note 1: 
T need not be Cpp17EqualityComparable.
— end note]
2
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Returns: If x.has_value() != y.has_value(), false; otherwise if x.has_value() == false, true; otherwise *x == *y.
3
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Remarks: Specializations of this function template for which *x == *y is a core constant expression are constexpr functions.
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template<class T, class U> constexpr bool operator!=(const optional<T>& x, const optional<U>& y);
4
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Mandates: The expression *x != *y is well-formed and its result is convertible to bool.
5
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Returns: If x.has_value() != y.has_value(), true; otherwise, if x.has_value() == false, false; otherwise *x != *y.
6
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Remarks: Specializations of this function template for which *x != *y is a core constant expression are constexpr functions.
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template<class T, class U> constexpr bool operator<(const optional<T>& x, const optional<U>& y);
7
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Mandates: *x < *y is well-formed and its result is convertible to bool.
8
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Returns: If !y, false; otherwise, if !x, true; otherwise *x < *y.
9
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Remarks: Specializations of this function template for which *x < *y is a core constant expression are constexpr functions.
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template<class T, class U> constexpr bool operator>(const optional<T>& x, const optional<U>& y);
10
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Mandates: The expression *x > *y is well-formed and its result is convertible to bool.
11
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Returns: If !x, false; otherwise, if !y, true; otherwise *x > *y.
12
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Remarks: Specializations of this function template for which *x > *y is a core constant expression are constexpr functions.
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template<class T, class U> constexpr bool operator<=(const optional<T>& x, const optional<U>& y);
13
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Mandates: The expression *x <= *y is well-formed and its result is convertible to bool.
14
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Returns: If !x, true; otherwise, if !y, false; otherwise *x <= *y.
15
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Remarks: Specializations of this function template for which *x <= *y is a core constant expression are constexpr functions.
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template<class T, class U> constexpr bool operator>=(const optional<T>& x, const optional<U>& y);
16
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Mandates: The expression *x >= *y is well-formed and its result is convertible to bool.
17
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Returns: If !y, true; otherwise, if !x, false; otherwise *x >= *y.
18
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Remarks: Specializations of this function template for which *x >= *y is a core constant expression are constexpr functions.
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template<class T, three_way_comparable_with<T> U> constexpr compare_three_way_result_t<T, U> operator<=>(const optional<T>& x, const optional<U>& y);
19
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Returns: If x && y, *x <=> *y; otherwise x.has_value() <=> y.has_value().
20
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Remarks: Specializations of this function template for which *x <=> *y is a core constant expression are constexpr functions.