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

Nullability and optionals in Objective-C


Objective-C provides a facility to work at compile time with nullability and optionals. While it's not as powerful as Swift optionals, it still provides a decent amount of safety for pure Objective-C programs. Lastly, it can be used to better interoperate with Swift.

Let's first consider this simple Objective-C interface:

@interface AnObject: NSObject

@property (nonatomic, copy) NSString* string;

@end

This is exposed in Swift as the following:

class AnObject: NSObject {
var string: String!
}

As you might notice, the string is a forced unpacked string, but this is unlikely what you would expect. Before Swift 4, the following code was valid but would crash at runtime:

// Swift 3
let object = AnObject()
let string = object.string // String!
string.appendContentsOf("SwiftObject") 
// fatal error: unexpectedly found nil while unwrapping an Optional value

Starting with Swift 4, however, the forced unpack optionals have not been accessible without using the ...