The equality operator.
The default behavior for all Objects is to return true if and
only if this and other are the same object.
Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:
Total: It must return a boolean for all arguments. It should never throw
or return null.
Reflexive: For all objects o, o == o must be true.
Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must
either both be true, or both be false.
Transitive: For all objects o1, o2, and o3, if o1 == o2 and
o2 == o3 are true, then o1 == o3 must be true.
The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.
If a subclass overrides the equality operator it should override the hashCode method as well to maintain consistency.
external bool operator ==(other);