Speed of NSArray#count

If I do

[myArray count]

is it O(1) or O(n), where n is the number of elements in the array?

The source code of Core Foundation collections (upon which Foundation collections are built) is open source. If you inspect CFArray.c, you’ll see that __CFArrayGetCount() is O(1).

If it is not O(1) then you should find another array implementation :)