Swift Programming: The Big Nerd Ranch Guide, 3rd Edition

Chapter 18. Value vs Reference Types

This chapter reviews and builds on the lessons you have been learning about value types (structs and enums) and reference types (classes). You will explore the differences between the two by comparing their differing behaviors in a variety of scenarios. At the end of this chapter, you should have a good understanding of when to use a value type or a reference type.

Value Semantics

Create a new macOS playground called ValueVsRefs. Your playground has the usual template code:

    import Cocoa
    
    var str = "Hello, playground"

You have seen this code many times before: You have a mutable instance of type String set to the value "Hello, playground". Make a new string by giving the value of str to another instance. ...