DevFright

When creating iPhone apps you will come across times when you can use single instance of a class across an entire app. Network manager, audio player, and other classes that Apple provides are called Singletons. It is one of the design patterns used in iOS app development.

A singleton ensures that only one instance of the class exists across the entire app. One example is App Settings, and another is a connection to a database where you probably want just a single connection.

Although singletons are relatively easy to create, meaning the syntax to allow a class to be a singleton, you need to be careful how you create it to avoid tight coupling and hidden dependencies.

A class in Swift, like classes in other programming languages, serves as a blueprint for creating objects that encapsulate data and behaviour. In Swift, you will see both classes and structs. This post will primarily focus on classes, although I will mention structs throughout to highlight some of the differences.

Classes are reference types, meaning that if you instantiate it, and then make a copy of it, any changes to either copy will be reflected in the other copy.

class Car {
    var model: String
    init(model: String) {
        self.model = model
    }
}

let car1 = Car(model: "Ferrari")
let car2 = car1
car2.model = "Lamborghini"

print(car1.model)

Although we changed car2’s model, because car2 is a copy of car1, and that it copies by reference, any changes to car2 here will also be changing car1.