This class extends the functionality of NSMutableSet by associating with each member of the set a count of how many times the object has been added to the set. By keeping a count with each object, NSCountedSet essentially removes the restriction that every member of a set must be unique. NSCountedSet reimplements several of NSMutableSet's methods to support the object counter. The one new method in NSCountedSet is countForObject:, which will return the counter value for the specified object. If the object is not a member of the set, this method returns 0. This count can be viewed as the number of occurences of the object within the set.

@interface NSCountedSet : NSMutableSet
// Initializers
- (id)initWithArray:(NSArray *)array;
- (id)initWithCapacity:(unsigned)numItems;
- (id)initWithSet:(NSSet *)set;
// Instance Methods
- (void)addObject:(id)object;
- (unsigned)countForObject:(id)object;
- (NSEnumerator *)objectEnumerator;
- (void)removeObject:(id)object;