Automatic Reference Counting
Swift uses Automatic Reference Counting (ARC) to track and manage your app’s memory
usage. In most cases, this means that memory management “just works” in Swift, and
you do not need to think about memory management yourself. ARC automatically frees
up the memory used by class instances when those instances are no longer needed.
However, in a few cases ARC requires more information about the relationships between
parts of your code in order to manage memory for you. This chapter describes those
situations and shows how you enable ARC to manage all of your app’s memory.