SALE: Save 50% on all my books and bundles >>

What is a singleton?

Swift version: 5.1

Paul Hudson    @twostraws   

Singletons are objects that should only ever be created once, then shared everywhere they need to be used. They are common on Apple’s platforms: FileManager, UserDefaults, UIApplication, and UIAccelerometer are all mostly used through their singleton implementations.

The basic implementation of a Swift singleton looks like this:

struct Settings {
    static let shared = Settings()
    var username: String?

    private init() { }
}

Adding an initializer to the Settings struct automatically disables the default memberwise initializer, and it’s marked private so that it also can’t be called from outside the class. However, the struct creates an instance of itself as a static variable, which means the only instance of the Settings struct is the one it created: Settings.shared.

Hacking with Swift is sponsored by Instabug

SPONSORED Catch bugs as soon as they happen and know exactly why a crash occurred by integrating Instabug's SDK in one minute. You will automatically receive device data, network logs, and reproduction steps with every bug and crash report.

Learn more and get started for free

Sponsor Hacking with Swift and reach the world's largest Swift community!

Cascable unleashes the power of your camera and unlocks powerful workflows for shooting, managing, and geotagging your photos.

Available from iOS 8.0 – learn more in my book Swift Design Patterns

Similar solutions…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

BUY OUR BOOKS
Buy Pro Swift Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Average rating: 2.9/5