operator==, <=>(std::reference_wrapper)

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Old binders and adaptors
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std::reference_wrapper
friend constexpr bool
    operator== ( reference_wrapper lhs, reference_wrapper rhs ) ;
(1) (since C++26)
friend constexpr bool
    operator== ( reference_wrapper lhs, reference_wrapper< const T> rhs ) ;
(2) (since C++26)
friend constexpr bool
    operator== ( reference_wrapper lhs, const T& ref ) ;
(3) (since C++26)
friend constexpr auto
    operator<=> ( reference_wrapper lhs, reference_wrapper rhs ) ;
(4) (since C++26)
friend constexpr auto
    operator<=> ( reference_wrapper lhs, reference_wrapper< const T> rhs ) ;
(5) (since C++26)
friend constexpr auto
    operator<=> ( reference_wrapper lhs, const T& ref ) ;
(6) (since C++26)

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()
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
4,5) Compares two reference_wrapper objects using synth-three-way
4) This overload participates in overload resolution only if the expression synth-three-way (lhs.get ( ), rhs.get ( ) )
5) This overload participates in overload resolution only if all following conditions are satisfied:
6) Compares reference_wrapper object with a reference using synth-three-way
This overload participates in overload resolution only if the expression synth-three-way (lhs.get(), ref)

The <, <=, >, >=, and != operators are synthesized from operator<=> and operator==

Parameters

lhs, rhs - reference_wrapper object to compare
ref - reference to compare to the reference_wrapper object

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)

Exceptions

Throws when and what the comparison throws.

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>

Feature-test macro Value Std Feature
__cpp_lib_reference_wrapper 202403L (C++26) Comparisons for std::reference_wrapper

Example

This section is incomplete
Reason: no example
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