Other than adding dozens of methods to NSArray/MutableArray for each "generic" you define and limiting my choice of collection to an array (rather than a set or

Other than adding dozens of methods to NSArray/MutableArray for each "generic" you define and limiting my choice of collection to an array (rather than a set or dictionary), why would you use this rather than define your own collection class that keeps the underlying store encapsulated and enforces its own type-safety? If type-safety is that important, a custom collection class will enrich your domain model and be more obvious.