Stumbled upon on very good deep dive into NSMutableArray implementation. When I just started working on iOS and MacOS development, somebody told me that NSMutableArray is based on a circular buffer, so it’s very efficient for queues and stacks as well. I remembered that and as 99% of engineers never really cared about details. Besides, Apple never released sources for its core classes. However curious minds, as usual, got to the bottom of the issue.