 Solution

With the completed default trait from part (a), the expression is well-typed and creates the empty complete multiset, provided the type T is in scope. Every member has a concrete default, entries is empty, and every count is zero.

With only the originally printed abstract trait, it is not a legal instantiation, because abstract queries and operations remain unimplemented. The distinction is whether part (a)'s supplied defaults are in force, rather than any special treatment of anonymous objects.