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 visitor pattern


When building complex algorithms, it is practical to separate the algorithm from the objects it operates on. The visitor pattern helps achieve such separation. One of the direct effects of using the visitor pattern is the ability to implement multiple distinct operations, without changing the underlying object structure.

The visitor pattern can be described through the series of protocols that each object has to implement:

  1. Define a Visitable protocol. Elements that can be visited implement this protocol.
  2. Define a Visitor protocol. Visitor objects implement this protocol, which helps them traverse Visitable objects.
  3. Extend existing objects to be Visitable.
  4. Implement one or many Visitor objects and their logic.

Visitable and visitor protocols

Thanks to Swift and its expressive generics, it is possible to abstract the visitor pattern through a series of protocols:

protocol Visitor {
func visit<T>(element: T) whereT:Visitable
}

A Visitor is an object that can traverse Visitable...