Book Image

Swift 3 Object-Oriented Programming - Second Edition

By : Gaston C. Hillar
Book Image

Swift 3 Object-Oriented Programming - Second Edition

By: Gaston C. Hillar

Overview of this book

Swift has quickly become one of the most-liked languages and developers’ de-facto choice when building applications that target iOS and macOS. In the new version, the Swift team wants to take its adoption to the next level by making it available for new platforms and audiences. This book introduces the object-oriented paradigm and its implementation in the Swift 3 programming language to help you understand how real-world objects can become part of fundamental reusable elements in the code. This book is developed with XCode 8.x and covers all the enhancements included in Swift 3.0. In addition, we teach you to run most of the examples with the Swift REPL available on macOS and Linux, and with a Web-based Swift sandbox developed by IBM capable of running on any web browser, including Windows and mobile devices. You will organize data in blueprints that generate instances. You’ll work with examples so you understand how to encapsulate and hide data by working with properties and access control. Then, you’ll get to grips with complex scenarios where you use instances that belong to more than one blueprint. You’ll discover the power of contract programming and parametric polymorphism. You’ll combine generic code with inheritance and multiple inheritance. Later, you’ll see how to combine functional programming with object-oriented programming and find out how to refactor your existing code for easy maintenance.
Table of Contents (17 chapters)
Swift 3 ObjectOriented Programming - Second Edition
Credits
About the Author
Acknowledgement
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface

Downcasting with protocols and classes


The ComicCharacter protocol defines one of the method requirements for the drawSpeechBalloon method with destination as an argument of the ComicCharacter type, which is the same type that the protocol defines. The following is the first line in our sample code that called this method:

    brian.drawSpeechBalloon(destination: merlin, message: "How do you do?") 

We called the method defined within the AngryDog class because brian is an instance of AngryDog. We passed an AngryDog instance, merlin, to the destination argument. The method works with the destination argument as an instance that conforms to the ComicCharacter protocol; therefore, whenever we reference the destination variable, we will only be able to see what the ComicCharacter type defines.

We can easily understand what happens under the hood when Swift downcasts a type from its original type to a target type, such as a protocol to which the class conforms. In this case, AngryDog is downcasted...