Swift Programming: The Big Nerd Ranch Guide

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. An instance of a reference type, however, behaves differently in that these two actions actually create an additional reference to the same underlying instance.

Let’s add a new class to model a Greek god to the playground to see just what this means.

Listing 18.3  Adding a Greek god class

import Cocoa

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

class GreekGod {
    var name: String
    init(name: String) { ...