NSMutableIndexSet
A mutable collection of unique integer values that represent indexes in another collection.
Declaration
class NSMutableIndexSetOverview
In Swift, this type bridges to IndexSet; use NSMutableIndexSet when you need reference semantics or other Foundation-specific behavior.
The NSMutableIndexSet 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...(NSNotFound - 1); trying to use indexes outside this range is invalid.
The values in a mutable index set are always sorted, so the order in which values are added is irrelevant.
Do not subclass the NSMutableIndexSet class.