What's the difference between NSIndexSet and NSSet?

Question

I'm a bit new to Cocoa and I was reading about NSIndexSet. Why is it necessary? It seems to me that NSIndexSet is nothing but a NSSet of integers, is that right? What's the purpose of creating a separate collection alltogether?

Answer 1

There are a couple reasons:

1. NSIndexSet stores unsigned integer primitive types, whereas NSSet stores objects.
2. NSIndexSet is optimized for storing unsigned integers, specifically a set of integers into another data structure like an NSArray.