Book Image

Hands-On Design Patterns with Swift

By : Florent Vilmart, Giordano Scalzo, Sergio De Simone
Book Image

Hands-On Design Patterns with Swift

By: Florent Vilmart, Giordano Scalzo, Sergio De Simone

Overview of this book

Swift keeps gaining traction not only amongst Apple developers but also as a server-side language. This book demonstrates how to apply design patterns and best practices in real-life situations, whether that's for new or already existing projects. You’ll begin with a quick refresher on Swift, the compiler, the standard library, and the foundation, followed by the Cocoa design patterns – the ones at the core of many cocoa libraries – to follow up with the creational, structural, and behavioral patterns as defined by the GoF. You'll get acquainted with application architecture, as well as the most popular architectural design patterns, such as MVC and MVVM, and learn to use them in the context of Swift. In addition, you’ll walk through dependency injection and functional reactive programming. Special emphasis will be given to techniques to handle concurrency, including callbacks, futures and promises, and reactive programming. These techniques will help you adopt a test-driven approach to your workflow in order to use Swift Package Manager and integrate the framework into the original code base, along with Unit and UI testing. By the end of the book, you'll be able to build applications that are scalable, faster, and easier to maintain.
Table of Contents (22 chapters)
Title Page
Copyright and Credits
About Packt
Contributors
Preface
Index

The singleton pattern 


The singleton pattern is one of the most used (and misused) creational patterns. It is seen throughout the Cocoa libraries, UIKit, AppKit, and many other Apple frameworks. Be aware that its use can lead to a central state point that gets mutated across your whole program, which can lead to nasty bugs.

In this section, we'll go back to basics with the singleton and focus on its use cases.

Using singletons

Singletons are fairly easy in Swift. A singleton is an object of which there can never be more than one instance in your program. The first instance of a singleton object will be the last. As a corollary, singletons never die, and their lifespan is always your whole program.

In Swift, we have to be particularly cautious about retain cycles. Any object that will be retained by your singleton will ultimately live till the end of your program. It's not an understatement to say: you have to be very cautious with them.

Here's an example:

class Earth {

    static let current...