The type must work with == operator and the result should have standard semantics.
The type T
satisfies EqualityComparable if.
Given.
a
, b
, and c
, expressions of type T
or 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:
|
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 C++ 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)
.
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http://en.cppreference.com/w/cpp/named_req/EqualityComparable