Does NSMutableArray actually count the items every time its count method is called?

Question

Because of cocoa design patterns, the name of the instance method count in NSMutableArray is ambiguous; it could either return a saved variable

Answer 1

As you have correctly noted, there is no guarantee that it will behave one way or the other.

In practice, though, -[NSArray count] is a constant-time operation. You can confirm this yourself by creating a small array and a large array and benchmarking the time it takes to get their counts. It would be pretty silly to have an O(n) count method on the core array classes like this.