Концепции C++: EqualityComparable — cppreference.com

Материал из cppreference.com

The type must work with == operator and the result should have standard semantics.

Expression	Requirements	Return type
`a == b`	Commutativity (`a == b` yields the same as `b == a`) Transitivity (if `a == b` and `b == c`, then `a == c`)	`bool` or a type implicitly convertible to `bool`