operator==, <=>(std::reference_wrapper)
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std::reference_wrapper
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operator==operator<=>
(C++26)(C++26)
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friend constexpr bool
operator==( reference_wrapper lhs, reference_wrapper rhs );
(1)
(since C++26)
operator==( reference_wrapper lhs, reference_wrapper rhs );
friend constexpr bool
operator==( reference_wrapper lhs, reference_wrapper<const T> rhs );
(2)
(since C++26)
operator==( reference_wrapper lhs, reference_wrapper<const T> rhs );
friend constexpr bool
operator==( reference_wrapper lhs, const T& ref );
(3)
(since C++26)
operator==( reference_wrapper lhs, const T& ref );
friend constexpr auto
operator<=>( reference_wrapper lhs, reference_wrapper rhs );
(4)
(since C++26)
operator<=>( reference_wrapper lhs, reference_wrapper rhs );
friend constexpr auto
operator<=>( reference_wrapper lhs, reference_wrapper<const T> rhs );
(5)
(since C++26)
operator<=>( reference_wrapper lhs, reference_wrapper<const T> rhs );
friend constexpr auto
operator<=>( reference_wrapper lhs, const T& ref );
(6)
(since C++26)
operator<=>( reference_wrapper lhs, const T& ref );
Performs comparison operations on reference_wrapper objects.
1,2) Compares two
reference_wrapper objects. The objects compare equal if and only if lhs.get() and rhs.get() are equal.1) This overload participates in overload resolution only if the expression lhs.get() == rhs.get() is well-formed and its result is convertible to bool.
2) This overload participates in overload resolution only if all following conditions are satisfied:
- std::is_const_v <T> is false.
- The expression lhs.get() == rhs.get() is well-formed and its result is convertible to bool.
3) Compares
reference_wrapper object with a reference. The parameters compare equal if and only if lhs.get() is equal to ref. This overload participates in overload resolution only if the expression lhs.get() == ref is well-formed and its result is convertible to bool.
4) This overload participates in overload resolution only if the expression synth-three-way (lhs.get(), rhs.get()) is well-formed.
5) This overload participates in overload resolution only if all following conditions are satisfied:
- std::is_const_v <T> is false.
- The expression synth-three-way (lhs.get(), rhs.get()) is well-formed.
This overload participates in overload resolution only if the expression synth-three-way (lhs.get(), ref) is well-formed.
The <, <=, >, >=, and != operators are synthesized from operator<=> and operator== respectively.
[edit] Parameters
lhs, rhs
-
reference_wrapper object to compare
ref
-
reference to compare to the
reference_wrapper object
[edit] Return value
1,2) lhs.get() == rhs.get().
3) lhs.get() == ref.
4,5) synth-three-way (lhs.get(), rhs.get()).
6) synth-three-way (lhs.get(), ref).
[edit] Exceptions
Throws when and what the comparison throws.
[edit] Notes
The return types of operator<=> are deduced from return statements to avoid hard error when instantiating a std::reference_wrapper <T> with synth-three-way-result<T> being ill-formed.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_reference_wrapper |
202403L |
(C++26) | Comparisons for std::reference_wrapper
|
[edit] Example
This section is incomplete
Reason: no example
Reason: no example