Difference between revisions of "cpp/utility/functional/reference wrapper/basic common reference"
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Andreas Krug (Talk | contribs) m (fmt) |
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template< class R, class T, | template< class R, class T, | ||
template<class> RQual, template<class> TQual > | template<class> RQual, template<class> TQual > | ||
| − | + | requires (/*ref-wrap-common-reference-exists-with*/<R, T, RQual<R>, TQual<T>> && | |
| − | + | !/*ref-wrap-common-reference-exists-with*/<T, R, TQual<T>, RQual<R>>) | |
struct basic_common_reference<R, T, RQual, TQual>; | struct basic_common_reference<R, T, RQual, TQual>; | ||
}} | }} | ||
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template< class T, class R, | template< class T, class R, | ||
template<class> TQual, template<class> RQual > | template<class> TQual, template<class> RQual > | ||
| − | + | requires (/*ref-wrap-common-reference-exists-with*/<R, T, RQual<R>, TQual<T>> && | |
| − | + | !/*ref-wrap-common-reference-exists-with*/<T, R, TQual<T>, RQual<R>>) | |
struct basic_common_reference<T, R, TQual, RQual>; | struct basic_common_reference<T, R, TQual, RQual>; | ||
}} | }} | ||
Latest revision as of 00:37, 4 January 2024
| Defined in header <functional>
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template< class R, class T, template<class> RQual, template<class> TQual > |
(1) | (since C++23) |
| template< class T, class R, template<class> TQual, template<class> RQual > |
(2) | (since C++23) |
| Helper concepts |
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| template< class R, class T, class RQ, class TQ > concept /*ref-wrap-common-reference-exists-with*/ = |
(3) | (exposition only*) |
The common reference type of a reference_wrapper (denoted as R) and a type T, correspondingly applied with cv and reference qualifiers (denoted as RQ and TQ respectively), is equivalent to a common reference type of underlying type of R applied with lvalue reference and the TQ.
The common reference type is defined only if R is the only reference_wrapper, the underlying type of R applied with lvalue reference and the TQ have a common reference type to which RQ must be convertible.
The exposition-only constant /*is-ref-wrapper*/<R> is true if and only if R is a specialization of std::reference_wrapper.
Contents |
[edit] Member types
| Member type | Definition |
type
|
std::common_reference_t<typename R::type&, TQual<T>> (1,2) |
[edit] Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_common_reference_wrapper |
202302L | (C++23) | Make std::common_reference_t of std::reference_wrapper a reference type |
[edit] Example
#include <concepts> #include <functional> static_assert(std::same_as<std::common_reference_t<int&, std::reference_wrapper<int>>, int&>); static_assert(std::same_as<std::common_reference_t<std::reference_wrapper<int>&, int&>, int&>); static_assert(std::same_as<std::common_reference_t<int&, const std::reference_wrapper<int>&>, int&>); int main() {}
[edit] See also
| determines the common reference type of a group of types (class template) |
