iOS 14 Programming Fundamentals with Swift

Chapter 12. Memory Management

Classes, both in Swift and in Objective-C, are reference types (see “Value Types and Reference Types”). Behind the scenes, Swift and Objective-C memory management for reference types works essentially the same way. Such memory management, as I pointed out in Chapter 5, can be a tricky business.

Fortunately, Swift uses ARC (automatic reference counting), so you don’t have to manage the memory for every reference type object explicitly and individually, as was once necessary in Objective-C. Thanks to ARC, you are far less likely to make a memory management mistake, and more of your time is liberated to concentrate on what your app actually does instead of dealing with memory management concerns.

Still, even in Swift, and even with ARC, it is possible to make a memory management mistake, or to be caught unawares by Cocoa’s memory management behavior. A memory management mistake can lead to runaway excessive memory usage, crashes, or mysterious misbehavior of your app. Cocoa memory management can be surprising in individual cases, and can mislead you into making a memory management mistake; so you need to understand, and prepare for, what Cocoa is going to do.

Principles of Cocoa Memory Management

The reason why reference type memory must be managed at all is that references to reference type objects are merely pointers to the actual object, and there can be multiple references (pointers) to the very same object. This means that every reference must ...