Concept: Reference-equatable type
A reference-equatable type is a type that uses reference equality, not value equality.
Interfaces, pointers, delegates, and of course value types (including enumerations) are not reference-equatable. However, types derived from interfaces may be reference-equatable.
Any base class of a reference-equatable type is also a reference-equatable type. However, a class derived from a reference-equatable type may or may not be reference-equatable.
The concept of a "reference-equatable type" by itself is not very useful; it is used in the definition of the
reference-equatable instance concept
, which is much more useful.