Question

For some odd reason NSOrderedSet does not appear to be implemented in iOS. Is there another object that gives similar functionality — basically the ability to insert/remove objects randomly and access the first/last in sort order?

It seems to me that something like this would be needed in order to implement basic FIFO queues and the like.

Edit: I ended up doing an RYO solution.

Answer 1

One option is this open source data structures library:
http://dysart.cs.byu.edu/CHDataStructures/index.html

In that library is a CHOrderedSet
http://dysart.cs.byu.edu/CHDataStructures/interface_c_h_ordered_set.html

It’s only dependency is NSMutableSet so it should work across all your iOS versions.

EDIT:

As Bourne pointed out above, it’s also in iOS5 (reference):

The new NSOrderedSet collection class offers the semantics of sets,
whereby each element occurs at most once in the collection, but where
elements are in a specific order.

CHOrderedSet is a good option if you don’t have a hard dependency on iOS5.