C++ named requirements: EqualityComparable

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 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: For all values of a, a == a yields true. If a == b, then b == a If a == b and b == c, then a == c

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 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).

See also

equality_comparableequality_comparable_with (C++20)

specifies that operator == is an equivalence relation (concept)