Question

How is NSMutableArray implemented?

If there are a number of NSMutableArray references to a mutable array e.g. Source Array and each of these pointing arrays sort the objects differently, are the objects copied over into each array or are the object pointers just internally rearranged?

If the source array is updated with new objects, will the NSMutableArray pointers automatically add an the entry to their internal reference.

Answer 1

It just stores pointers.This means that if the NSMutableArray stores immutable objects, then you are sure that they’ll not change their state, but if it has a mutable object the state of any referenced object may change at any time.
Exactly I don’t know how it’s implemented, but I would say a pointer to id.It allocates memory and then update the id at the index that needs:

id* pointers;
< Allocation>
pointers[i]= newObjectPointer;