NSMutable class represents a mutable collection of unique unsigned integers, known as indexes because of the way they are used. This collection is referred to as a mutable index set. The inclusive range of valid indexes is
0...(NSNot; trying to use indexes outside this range is invalid.
- iOS 2.0+
- macOS 10.3+
- tvOS 9.0+
- watchOS 2.0+
The values in a mutable index set are always sorted, so the order in which values are added is irrelevant.
You must not subclass the