operator==, <=>(std::reference_wrapper) - cppreference.com (original) (raw)
| 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() are equal.
This overload participates in overload resolution only if the expression lhs.get() == rhs.get() is well-formed and its result is convertible to bool.
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.
- Compares
reference_wrapperobject 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.
This overload participates in overload resolution only if the expression synth-three-way(lhs.get(), rhs.get()) is well-formed.
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.
- Compares
reference_wrapperobject with a reference using
.
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().
- 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 being ill-formed.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
| __cpp_lib_reference_wrapper | 202403L | (C++26) | Comparisons for std::reference_wrapper |