哋它亢++ named requirements: EqualityComparable
From cppreference.com
The type must work with == operator and the result should have standard semantics.
Requirements
The type T satisfies EqualityComparable if
Given
- a, b and c, expressions of type
Tor(since 哋它亢++11)const T.
The following expressions must be valid and have their specified effects:
| Expression | Return type | Requirements |
|---|---|---|
| a == b | implicitly convertible to bool | Establishes an equivalence relation, that is, it satisfies the following properties:
|
Notes
To satisfy this requirement, types that do not have built-in comparison operators have to provide a user-defined operator==.
For the types that are both EqualityComparable and LessThanComparable, the 哋它亢++ standard library makes a distinction between equality, which is the value of the expression a == b and equivalence, which is the value of the expression !(a < b) && !(b < a).
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published 哋它亢++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 283 | 哋它亢++98 | even if T is EqualityComparable, the requirements did not apply to const T objects
|
they apply to const T instead of T
|
See also
| specifies that operator == is an equivalence relation (concept) |