Learning Swift, 3rd Edition

Chapter 3. Object-Oriented Development in Swift

The previous chapter introduced the basic building blocks of programming in Swift. In this chapter, we’re going to look at some of the more advanced features, such as classes and structs, memory management, working with files and external data, and error handling. We’ll also touch on interoperating with Apple’s older programming language, Objective-C.

Swift is a multiparadigm language, and can work with a variety of different programming language styles. This means it can be used as an object-oriented programming language, where you do the majority of your work by creating and manipulating objects—chunks of data and code that represent a thing that can perform some useful work or store some useful data.

Classes and Objects

In Swift, as in Objective-C, Java, and C++ (and many other languages), you define templates for your objects using classes. Classes in Swift look like this:

class Vehicle {

}

Note

Each programming language (and its associated libraries) has its own particular take on object orientation. The approach that Swift and Cocoa take is that using extensions and protocols is a better idea most of the time than subclassing.

Classes contain both properties and methods. Properties are variables that are part of a class, and methods are functions that are part of a class. The Vehicle class in the following example contains two properties: an optional String called color, and an Int called maxSpeed. Property declarations ...