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

Reference Semantics

Reference semantics work differently than value semantics. With value types, you get a copy of the instance when you assign it to a new constant or variable. The same is true when you pass an instance of a value type as the argument to a function. But for an instance of a reference type, these two actions create an additional reference to the same underlying instance.

To see what this means, you are going to model a company and its employees, who for some reason have a hard time keeping their employee IDs straight. Add a new class to the playground to model a company’s employee:

Example 18.3. Adding an Employee class

...
playgroundGreeting += "! How are you today?"               "Hello, playground! How...
str                                                        "Hello, playground"

class ...