7. Everything Is Connected – Memory Management | Learning Swift Second Edition

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Table Of Contents

Learning Swift Second Edition - Second Edition

By : Andrew J Wagner

5 (1)

Learning Swift Second Edition

5 (1)

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.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Free Chapter

1. Introducing Swift

1. Introducing Swift

Defining our goals for this book

Setting up the development environment

Running our first swift code

Understanding playgrounds

Learning with this book

Summary

2. Building Blocks – Variables, Collections, and Flow Control

2. Building Blocks – Variables, Collections, and Flow Control

Core Swift types

Swift's type system

Printing to the console

Control flow

Functions

Bringing it all together

Summary

3. One Piece at a Time – Types, Scopes, and Projects

3. One Piece at a Time – Types, Scopes, and Projects

Structs

Classes

Enumerations

Projects

Extensions

Scope

Access control

Summary

4. To Be or Not To Be – Optionals

4. To Be or Not To Be – Optionals

Defining an optional

Unwrapping an optional

Optional chaining

Implicitly unwrapped optionals

Debugging optionals

The underlying implementation

Summary

5. A Modern Paradigm – Closures and Functional Programming

5. A Modern Paradigm – Closures and Functional Programming

Functional programming philosophy

Closures

Building blocks of functional programming in Swift

Lazy evaluation

Example

Summary

6. Make Swift Work For You – Protocols and Generics

6. Make Swift Work For You – Protocols and Generics

Protocols

Generics

Extending generics

Putting protocols and generics to use

Summary

7. Everything Is Connected – Memory Management

7. Everything Is Connected – Memory Management

Computer data storage

Value types versus reference types

Automatic reference counting

Strong reference cycles

Lost objects

Structures versus classes

Summary

8. Paths Less Traveled – Error Handling

8. Paths Less Traveled – Error Handling

Throwing errors

Handling errors

Cleaning up in error situations

Summary

9. Writing Code the Swift Way – Design Patterns and Techniques

9. Writing Code the Swift Way – Design Patterns and Techniques

What is a design pattern?

Behavioral patterns

Structural patterns

Creational patterns

Using associated values effectively

Extending system types to reduce code

Lazy properties

Summary

10. Harnessing the Past – Understanding and Translating Objective-C

10. Harnessing the Past – Understanding and Translating Objective-C

Swift's relationship to Objective-C

Background of Objective-C

Constants and variables

Containers

Control flow

Functions

Types

Projects

Calling Objective-C code from Swift

Using functions

Summary

11. A Whole New World – Developing an App

11. A Whole New World – Developing an App

Conceptualizing the app

Setting up the app project

Configuring the user interface

Running the app

Allowing picture taking

Temporarily saving a photo

Populating our photo grid

Refactoring to respect model-view-controller

Permanently saving a photo

Summary

12. What's Next? – Resources, Advice, and the Next Steps

12. What's Next? – Resources, Advice, and the Next Steps

Apple's documentation

Forums and blogs

Prominent figures

Podcasts

Summary

Index

Index

Lost objects

It is a great idea to always keep strong reference cycles in mind, but if we are too aggressive with the use of weak and unowned references, we can run into the opposite problem, where an object is deleted before we intended it to be.

Between objects

With an object this will happen if all of the references to the object are weak or unowned. This won't be a fatal mistake if we use weak references, but if this happens with an unowned reference it will crash your program.

For example, let's look at the preceding example with an extra weak reference:

class SteeringWheel {
    weak var car: Car?
}
class Car {
    weak var steeringWheel: SteeringWheel!

    init(steeringWheel: SteeringWheel) {
        self.steeringWheel = steeringWheel
        steeringWheel.car = self
    }
}

let wheel = SteeringWheel()
let car = Car(steeringWheel: wheel)

This code is the same as the preceding one except that both the car property of SteeringWheel and the steeringWheel property of Car are weak. This means...

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