Ref

A Ref that is never equal to anything, including itself.

Use for MemoryObservables of mutable values (I mean, if your observable emits the same mutable value when it updates, instead of emitting a new immutable value)

A Ref that is only equal if the values match referentially

Use for MemoryObservables of large immutable Maps or Lists to improve performance (otherwise their equals method would iterate through the whole map / list to find differences)