Namespaces
Variants
Views
Actions

Difference between revisions of "cpp/concepts/common reference with"

From cppreference.com
< cpp‎ | concepts
m (→‎See also: P1754R1)
(+References)
 
(4 intermediate revisions by 4 users not shown)
Line 1: Line 1:
−
{{cpp/title|common_reference_with}}
+
{{cpp/title|common_reference_with {{mark since c++20}}}}
 
{{cpp/concepts/navbar}}
 
{{cpp/concepts/navbar}}
 
{{ddcl|header=concepts|since=c++20|1=
 
{{ddcl|header=concepts|since=c++20|1=
−
template < class T, class U >
+
template< class T, class U >
 
concept common_reference_with =
 
concept common_reference_with =
−
  std::same_as<std::common_reference_t<T, U>, std::common_reference_t<U, T>> &&
+
    std::same_as<std::common_reference_t<T, U>, std::common_reference_t<U, T>> &&
−
  std::convertible_to<T, std::common_reference_t<T, U>> &&
+
    std::convertible_to<T, std::common_reference_t<T, U>> &&
−
  std::convertible_to<U, std::common_reference_t<T, U>>;
+
    std::convertible_to<U, std::common_reference_t<T, U>>;
 
}}
 
}}
 
The concept {{tt|common_reference_with<T, U>}} specifies that two types {{tt|T}} and {{tt|U}} share a ''common reference type'' (as computed by {{lc|std::common_reference_t}}) to which both can be converted.
 
The concept {{tt|common_reference_with<T, U>}} specifies that two types {{tt|T}} and {{tt|U}} share a ''common reference type'' (as computed by {{lc|std::common_reference_t}}) to which both can be converted.
  
−
=== Semantic requirements ===
+
===Semantic requirements===
−
T and U model {{tt|common_reference_with<T, U>}} only if, given equality-preserving expressions {{tt|t1}}, {{tt|t2}}, {{tt|u1}} and {{tt|u2}} such that {{c|decltype((t1))}} and {{c|decltype((t2))}} are both {{tt|T}} and {{c|decltype((u1))}} and {{c|decltype((u2))}} are both {{tt|U}},
+
T and U model {{co|std::common_reference_with<T, U>}} only if, given [[cpp/concepts#Equality preservation|equality-preserving]] expressions {{tt|t1}}, {{tt|t2}}, {{tt|u1}} and {{tt|u2}} such that {{c|decltype((t1))}} and {{c|decltype((t2))}} are both {{tt|T}} and {{c|decltype((u1))}} and {{c|decltype((u2))}} are both {{tt|U}},
 
* {{c|std::common_reference_t<T, U>(t1)}} equals {{c|std::common_reference_t<T, U>(t2)}} if and only if {{tt|t1}} equals {{tt|t2}}; and
 
* {{c|std::common_reference_t<T, U>(t1)}} equals {{c|std::common_reference_t<T, U>(t2)}} if and only if {{tt|t1}} equals {{tt|t2}}; and
 
* {{c|std::common_reference_t<T, U>(u1)}} equals {{c|std::common_reference_t<T, U>(u2)}} if and only if {{tt|u1}} equals {{tt|u2}}.
 
* {{c|std::common_reference_t<T, U>(u1)}} equals {{c|std::common_reference_t<T, U>(u2)}} if and only if {{tt|u1}} equals {{tt|u2}}.
  
−
In other words, the conversion to the common reference type must preserve equality.
+
In other words, the conversion to the common reference type must [[cpp/concepts#Equality preservation|preserve equality]].
  
−
{{cpp/concepts/equality preservation|skip-requires=yes}}
+
===References===
 +
{{ref std c++23}}
 +
{{ref std|section=18.4.5|title=Concept {{tt|common_reference_with}}|id=concept.commonref}}
 +
{{ref std end}}
 +
{{ref std c++20}}
 +
{{ref std|section=18.4.5|title=Concept {{tt|common_reference_with}}|id=concept.commonref}}
 +
{{ref std end}}
  
−
=== See also ===
+
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
 
{{dsc inc|cpp/types/dsc common_reference}}
 
{{dsc inc|cpp/types/dsc common_reference}}

Latest revision as of 10:02, 7 September 2024

 
C++
 
Concepts library
Exposition-only concepts
 (C++20)
 
Defined in header <concepts>
template< class T, class U >

concept common_reference_with =
    std::same_as<std::common_reference_t<T, U>, std::common_reference_t<U, T>> &&
    std::convertible_to<T, std::common_reference_t<T, U>> &&

    std::convertible_to<U, std::common_reference_t<T, U>>;
 (since C++20)

The concept common_reference_with<T, U> specifies that two types T and U share a common reference type (as computed by std::common_reference_t) to which both can be converted.

[edit] Semantic requirements

T and U model std::common_reference_with<T, U> only if, given equality-preserving expressions t1, t2, u1 and u2 such that decltype((t1)) and decltype((t2)) are both T and decltype((u1)) and decltype((u2)) are both U,

In other words, the conversion to the common reference type must preserve equality.

[edit] References

  • C++23 standard (ISO/IEC 14882:2024):
  • 18.4.5 Concept common_reference_with [concept.commonref]
  • C++20 standard (ISO/IEC 14882:2020):
  • 18.4.5 Concept common_reference_with [concept.commonref]

[edit] See also

(C++20)
 determines the common reference type of a group of types
(class template) [edit]
(C++20)
 specifies that two types share a common type
(concept) [edit]
(C++11)
 determines the common type of a group of types
(class template) [edit]
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/concepts/common_reference_with&oldid=175811"