same abstract method
Will return true only if the collections internals are the same instances
(comparing by identity). This will be fast even for very large
collections, since it doesn't compare each item.
Note: This is not the same as identical(col1, col2) since it doesn't
compare the collection instances themselves, but their internal state.
Comparing the internal state is better, because it's also fast but will
return true more often.
Implementation
bool same(C other);