Book Image

Learning Swift Second Edition - Second Edition

By : Andrew J Wagner
Book Image

Learning Swift Second Edition - Second Edition

By: Andrew J Wagner

Overview of this book

Swift is Apple’s new programming language and the future of iOS and OS X app development. It is a high-performance language that feels like a modern scripting language. On the surface, Swift is easy to jump into, but it has complex underpinnings that are critical to becoming proficient at turning an idea into reality. This book is an approachable, step-by-step introduction into programming with Swift for everyone. It begins by giving you an overview of the key features through practical examples and progresses to more advanced topics that help differentiate the proficient developers from the mediocre ones. It covers important concepts such as Variables, Optionals, Closures, Generics, and Memory Management. Mixed in with those concepts, it also helps you learn the art of programming such as maintainability, useful design patterns, and resources to further your knowledge. This all culminates in writing a basic iOS app that will get you well on your way to turning your own app ideas into reality.
Table of Contents (19 chapters)
Learning Swift Second Edition
Credits
About the Author
About the Reviewer
www.PacktPub.com
Preface
Index

Lazy properties


One feature we have not yet discussed is the concept of lazy properties. Marking a property as lazy allows Swift to wait to initialize it until the first time it is accessed. This can be useful in at least a few important ways.

Avoiding unnecessary memory usage

The most obvious way to use lazy properties is to avoid unnecessary memory usage. Let's look at a very simple example first:

struct MyType {
    lazy var largeString = "Some String"
}
let instance = MyType()

Even though we created a new instance of MyType in the preceding code, largeString is not set until we try to access it. This is great if we have a large variable that may not be needed on every instance. Until it is accessed, it is not taking up any memory.

Avoiding unnecessary processing

We can also take this idea of a lazy property even further using a closure to calculate the value:

class Directory {
    lazy var subFolders: [Directory] = {
        var loaded = [Directory]()
        // Load subfolders into 'loaded...