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- Herausgeber: Packt Publishing
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Embrace the Protocol-Oriented Programming paradigm, for better code maintainability and increased performance, with Swift programming.
Key Features
- Leverage the power of Protocol-Oriented Programming in your applications
- Leverage generics to create very flexible frameworks
- Learn how to implement common design patterns in a protocol-oriented way
Book Description
Protocol-oriented programming is an incredibly powerful concept at the heart of Swift's design. Swift's standard library was developed using POP techniques, generics, and first-class value semantics; therefore, it is important for every Swift developer to understand these core concepts and take advantage of them. The fourth edition of this book is improved and updated to the latest version of the Swift programming language.
This book will help you understand what protocol-oriented programming is all about and how it is different from other programming paradigms such as object-oriented programming. This book covers topics such as generics, Copy-On-Write, extensions, and of course protocols. It also demonstrates how to use protocol-oriented programming techniques via real-world use cases.
By the end of this book, you will know how to use protocol-oriented programming techniques to build powerful and practical applications.
What you will learn
- Learn the differences between object-oriented programming and protocol-oriented programming
- Understand why value types should be prioritized over reference types
- Delve into protocols, protocol inheritance, protocol composition, and protocol extensions
- Learn how to implement COW (Copy-On-Write) within your custom value types
- Understand how memory management works in Swift and how to avoid common pitfalls
- Design applications by starting with the protocol rather than the implementation
Who this book is for
This book is intended for Swift developers who have, at minimum an introductory knowledge of the Swift programming language and would like to understand how they can use Protocol-Oriented Programming techniques in their applications.
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Seitenzahl: 302
Veröffentlichungsjahr: 2019
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Swift Protocol-Oriented Programming Fourth Edition
Copyright © 2019 Packt Publishing
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Commissioning Editor:Kunal ChaudhariAcquisition Editor:Larissa PintoContent Development Editor:Arun NadarSenior Editor: Jack CummingsTechnical Editor:Jinesh TopiwalaCopy Editor: Safis EditingProject Coordinator:Kinjal BariProofreader: Safis EditingIndexer:Rekha NairProduction Designer:Shraddha Falebhai
First published: February 2016 Second edition: November 2016 Third edition: October 2017 Fourth edition: June 2019
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ISBN 978-1-78934-902-3
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Contributors
About the author
Jon Hoffman has over 20 years' experience in the field of Information Technology. Over those 20 years, Jon has worked in the system administration, network administration, network security, application development, and architecture arenas. Currently, he works as an Enterprise Software Manager at Syntech Systems. He has developed extensively for the iOS platform since 2008. This includes several apps that he has published in the App Store, apps that he has written for third parties, and numerous enterprise applications. Some of Jon's other interests are playing basketball, kayaking, and working out with his daughters. Jon also really enjoys Tae Kwon Do, where he and his oldest daughter earned their black belts together early in 2014 and are currently 3rd-degree Black Belts.
About the reviewers
Nikola Brežnjak is an engineer at heart and a jack of all trades. Currently, he's the director of engineering at Teltech, where he is responsible for the management, mentoring, and coaching of mobile app developers. He loves his job! He has written books on the Ionic framework and the MEAN stack, and has been a technical reviewer for a number of Packt books. He likes to help out on Stack Overflow, where he's a top contributor. He records a podcast called DevThink with his friend, Shawn Milochik, and runs a local meetup called MeCoDe.
Vinod Madigeri is a senior software engineer with expertise in full-stack app development. He received his master’s in computer science from the University of Utah in 2015. He has worked in several industries (telecommunications, game technologies, and consumer electronics) as a developer, team leader, and mentor, writing software—in C, C++, Python, Objective-C, and Swift—for macOS and iOS platforms.
Currently, he spends much of his time exploring machine learning as a skill to complement his software development efforts.
Vinod has also been a technical reviewer for Mastering Swift 5, Object–Oriented Programming with Swift, Hands-On Full-Stack Development with Swift, and Multiplayer Game Development with HTML5.
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Table of Contents
Title Page
Copyright and Credits
Swift Protocol-Oriented Programming Fourth Edition
About Packt
Why subscribe?
Contributors
About the author
About the reviewers
Packt is searching for authors like you
Preface
Who this book is for
What this book covers
To get the most out of this book
Download the example code files
Conventions used
Get in touch
Reviews
Starting with the Protocol
Protocol syntax
Defining a protocol
Property requirements
Method requirements
Optional requirements
Protocol inheritance
Protocol composition
Using protocols as a type
Polymorphism with protocols
Type casting with protocols
Associated types with protocols
Delegation
Designing with protocols
Protocols in the Swift standard library
Summary
Our Type Choices
Classes
Structures
Access controls
Enumerations
Tuples
Protocols
Value and reference types
Recursive data types for reference types only
Inheritance for reference types only
Dynamic dispatch
Swift's built-in types
COW
Summary
Extensions
Defining an extension
Protocol extensions
Text validation
Extensions with the Swift standard library
Conforming to the Equatable protocol
Summary
Generics
Generic functions
Type constraints with generics
Generic types
Associated types
Generic subscripts
COW
Generics in a protocol-oriented design
Generics in the Swift standard library
Summary
Memory Management
How ARC works
Strong reference cycles
Unowned references
Weak references
Summary
Object-Oriented Programming
What is object-oriented programming?
Requirements for the sample code
Swift as an object-oriented programming language
Class diagrams
Object-oriented design
Vehicle superclass
Vehicle subclasses
Polymorphism
Issues with object-oriented design
Summary
Protocol-Oriented Programming
Requirements for the sample code
Swift as a protocol-oriented programming language
Protocol inheritance
Protocol composition
Protocol extensions
The Vehicle protocol
Vehicle implementations
Summarizing protocol-oriented programming and object-oriented programming
Differences between object-oriented programming and protocol-oriented programming
Protocol and protocol extensions compared with superclasses
Implementing vehicle types
Using value and reference types
The winner is...
Summary
Adopting Design Patterns in Swift
What are design patterns?
Creational patterns
The singleton design pattern
Understanding the problem
Understanding the solution
Implementing the singleton pattern
The builder design pattern
Understanding the problem
Understanding the solution
Implementing the builder pattern
The factory method pattern
Understanding the problem
Understanding the solution
Implementing the factory method pattern
Structural design patterns
The bridge pattern
Understanding the problem
Understanding the solution
Implementing the bridge pattern
The facade pattern
Understanding the problem
Understanding the solution
Implementing the facade pattern
The proxy design pattern
Understanding the problem
Understanding the solution
Implementing the proxy pattern
Behavioral design patterns
The command design pattern
Understanding the problem
Understanding the solution
Implementing the command pattern
The strategy pattern
Understanding the problem
Understanding the solution
Implementing the strategy pattern
The observer pattern
Understanding the problem
Understanding the solution
Implementing the observer pattern
Summary
Case Studies
Logging services
Requirements
The design
Conclusion
The data access layer
Requirements
The design
The data model layer
The data helper layer
The bridge layer
Using the data-access layer
Conclusion
Summary
Other Books You May Enjoy
Leave a review - let other readers know what you think
Preface
Apple announced Swift 2 at the World Wide Developers Conference (WWDC) in 2015. They also declared that Swift was the world's first protocol-oriented programming language. Judging by the name, someone might assume that protocol-oriented programming is all about the protocol or is simply object-oriented programming under a different name. These assumptions would be wrong. Protocol-oriented programming is about so much more than just the protocol; it is actually a new way of not only writing applications but thinking about the design of our application.
In the first five chapters of this book, we take an in-depth look at each of the components of the protocol-oriented programming paradigm. These chapters are designed to give you a solid understanding of the different components of protocol-oriented programming, so that you can understand how to use these components in your applications. One of the biggest misconceptions about protocol-oriented programming is that it is just another name for object-oriented programming. In Chapter 6, Object-Oriented Programming, and Chapter 7, Protocol-Oriented Programming, we take on this myth by comparing protocol-oriented programming to object-oriented programming to see what is similar and what is different. We also discuss the advantages and disadvantages of both programming paradigms.
The last two chapters are written to help you understand how you can design your application in a protocol-oriented programming way. Chapter 8, Adopting Design Patterns in Swift, looks at how we can implement several design patterns in a protocol-oriented way, and Chapter 9, Case Studies, looks at three real-world case studies to reinforce everything previously discussed in the book.
Who this book is for
This book is intended for the developer who has at least an introductory knowledge of the Swift programming language and wants to understand what protocol-oriented programming is. This book is written for the developer who not only wants to understand protocol-oriented programming but also wants to fully understand the different components of the programming paradigm. This book is written for the developer who learns best by looking at and working with code, because every concept covered in the book is backed by example code written to give you a solid understanding of the current topic and to demonstrate how to properly implement it.
What this book covers
Chapter 1, Starting with the Protocol, looks at what protocols are and how they are used in the Swift programming language. We will also examine how protocols can be used to write very flexible and reusable code.
Chapter 2, Our Type Choices, discusses the different types that Swift offers (structs, classes, enums, and tuples). We will look at several examples of when to use the various types and when not to.
Chapter 3, Extensions, looks at how extensions and protocol extensions are used with the Swift programming language. We will look at examples of how extensions can be used with protocol-oriented programming.
Chapter 4, Generics, shows how powerful generics are. Apple has stated that Generics are one of the most powerful features of Swift. We will look at how to use Generics to make very flexible types, and also how to implement the Copy-on-Write (COW) feature for our custom types.
Chapter 5, Memory Management, looks at how Swift manages memory with Automatic Reference Counting (ARC) and how strong reference cycles can cause ARC to fail. We also look at how to use weak and unowned references.
Chapter 6, Object-Oriented Programming, examines how we would develop characters for a video game if we were taking an object-oriented approach. In order to really appreciate the ideas behind protocol-oriented programming, we need to understand the problems it is designed to solve. We will then look at the drawbacks with this design.
Chapter 7, Protocol-Oriented Programming, develops the same video game characters from Chapter 5, Memory Management, but this time we will take a protocol-oriented approach to the design. We will then compare the object-oriented approach and the protocol-oriented approach to see the advantages that the protocol-oriented approach offers.
Chapter 8, Adopting Design Patterns in Swift, looks at implementing several design patterns using protocol-oriented programming. For each of the design patterns, we will look at the problem they are designed to solve and how to implement the pattern.
Chapter 9, Case Studies, explores two case studies. This chapter is designed to pull everything from the first six chapters together to show you how to use protocol-oriented programming in real-world situations.
To get the most out of this book
To follow along with the examples in this book, you will need to have an Apple computer with OS X 10.14 or higher installed. You will also need to install Xcode version 10.2 or higher with Swift version 5 or higher. You should possess at least a basic knowledge of the Swift programming language and how to use the development tools on their environment.
Download the example code files
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The code bundle for the book is also hosted on GitHub at https://github.com/PacktPublishing/Swift-5-Protocol-Oriented-Programming-Fourth-Edition. In case there's an update to the code, it will be updated on the existing GitHub repository.
We also have other code bundles from our rich catalog of books and videos available at https://github.com/PacktPublishing/. Check them out!
Conventions used
There are a number of text conventions used throughout this book.
CodeInText: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: "To define the protocol, we use the protocol keyword, followed by the name of the protocol."
A block of code is set as follows:
struct MyStruct: MyProtocol { //Structure implementation here }
When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:
Initializing class with name One
Initializing class with name Two
Setting class1ref1 to nil
Releaseing class with name One
Setting class2ref1 to nil
Setting class2ref2 to nil
Releaseing class with name Two
Bold: Indicates a new term, an important word, or words that you see onscreen. For example, words in menus or dialog boxes appear in the text like this. Here is an example: "If we run this example, we will see that the Notification Received message."
Get in touch
Feedback from our readers is always welcome.
General feedback: If you have questions about any aspect of this book, mention the book title in the subject of your message and email us at [email protected].
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Starting with the Protocol
This book is all about protocol-oriented programming. When Apple announced Swift 2 at the World Wide Developers Conference (WWDC) in 2015, they also declared that Swift was the world's first protocol-oriented programming language. From its name, we may assume that protocol-oriented programming is all about the protocol; however, this would be incorrect. Protocol-oriented programming is about so much more than just the protocol; it's actually a new way of not only writing applications, but also how we think about application design.
In this chapter, you will learn about the following topics:
How to define property and functional requirements within a protocol
How to use protocol inheritance and composition
How to use a protocol as a type
What is
polymorphism?
How to use associated types with protocols
How to implement the delegation pattern with protocols
How to design type requirements with protocols
If you are coming from an object-oriented programming background, you may be familiar with the interface. In the object-oriented world, for most languages, the interface is a type that contains method and property signatures but does not contain implementation details. An interface can be considered a contract where any type that conforms to the interface must implement the required functionality defined within it. Most object-oriented developers rarely use interfaces as the focal point for their application design unless they are working with a framework similar to the Open Service Gateway Initiative (OSGi) framework. In protocol-oriented programming, the protocol is the focal point of your design.
When we are designing an application in an object-oriented way, we usually begin by focusing on the class hierarchy and how the objects interact. The object is a data structure that contains information about the attributes of the object in the form of properties, and the actions performed by or to the object in the form of methods. We cannot create an object without a blueprint that tells the application what attributes and actions to expect from the object. In most object-oriented languages, this blueprint comes in the form of a class. A class is a construct that allows us to encapsulate the properties and actions of an object into a single type.
Designing an application in a protocol-oriented way is significantly different from designing it in an object-oriented way. Rather than starting with the class hierarchy, protocol-oriented design says that we should start with the protocol. While protocol- oriented design is about so much more than just the protocol, we can think of the protocol as its backbone. After all, it would be pretty hard to have protocol-oriented programming without the protocol.
A protocol in Swift is similar to the interface in object-oriented languages, where the protocol acts as a contract that defines the methods, properties, and other requirements that are needed by our types to perform their tasks. We say that the protocol acts as a contract because any type that conforms to the protocol promises to implement the requirements defined by the protocol itself. If a type says that it conforms to a protocol and it doesn't implement all the functionality defined by the protocol, we will get a compile-time error and the project will not compile. In Swift, any class, structure, or enumeration can conform to a protocol.
We've just mentioned that the protocol is similar to the interface. Don't be fooled by this comparison because even though the interface and the protocol are similar, protocols in Swift are actually far more powerful than the interface in most object-oriented languages. As you read this book, you will find out how powerful Swift protocols can be.
Most modern object-oriented programming languages implement their standard library with a class hierarchy; however, the basis of Swift's standard library is the protocol (http://swiftdoc.org). Therefore, not only does Apple recommend that we use the protocol-oriented programming paradigm in our applications, but to also use it in the Swift standard library.
With the protocol being the basis of the Swift standard library and also the backbone of the protocol-oriented programming paradigm, it is very important that we fully understand what the protocol is and how we can use it. In this chapter, we will cover not only the basics of the protocol but also provide an understanding on how it can be used in application design.
Protocol syntax
In this section, we will look at how to define a protocol and how to add requirements to it. This will give us a basic understanding of the protocol. The rest of this chapter will build on this understanding.
Defining a protocol
The syntax we use to define a protocol is very similar to the syntax that's used to define a class, structure, or enumeration. The following example shows the syntax that's used to define a protocol:
protocol MyProtocol { //protocol definition here }
To define the protocol, we use the protocol keyword, followed by the name of the protocol. We then put the requirements, which our protocol defines, between curly brackets. Custom types can state that they conform to a particular protocol by placing the name of the protocol after the type's name, separated by a colon. The following example shows how we would define that a structure conforms to a protocol:
struct MyStruct: MyProtocol { //Structure implementation here }
A type can also conform to multiple protocols. We list the multiple protocols that the type conforms to by separating them with commas:
struct MyStruct: MyProtocol, AnotherProtocol, ThirdProtocol { //Structure implementation here }
Having a type conform to multiple protocols is a very important concept within protocol- oriented programming, as we will see later in this chapter and throughout this book. This concept is known as protocol composition. Now, let's see how we would add property requirements to our protocol.
Property requirements
A protocol can require that the conforming types provide certain properties with specified names and types. The protocol doesn't say whether the property should be a stored or computed property because the implementation details are left up to the conforming types.
When defining a property within a protocol, we must specify whether the property is a read-only or a read-write property by using the get and set keywords. We also need to specify the property's type since we cannot use type inference in a protocol. Let's look at how we would define properties within a protocol by creating a protocol named FullName, as shown in the following example:
protocol FullName { var firstName: String {get set} var lastName: String {get set} }
In this example, we define two properties named firstName and lastName, which are read-write properties. Any type that conforms to this protocol must implement both of these properties. If we wanted to define the property as read-only, we would define it using only the get keyword, as shown in the following code:
var readOnly: String {get}
It is possible to define static properties by using the static keyword, as shown in the following example:
static var typeProperty: String {get}
Static properties are properties that are owned by the type and shared by all instances. This means that if one instance changes the value of this property, then the value changes for all instances. We will look at how to use static instances more when we look at the singleton pattern.
Now, let's look at how we would add method requirements to our protocol.
Method requirements
A protocol can require that the conforming types provide specific methods. These methods are defined within the protocol exactly as we define them within a class or structure, but without the curly brackets and method body. We can define that these methods are instance or type methods using the static keyword. Adding default values to the method's parameters is not allowed when defining the method within a protocol.
Let's add a method named getFullName() to the FullName protocol:
protocol FullName { var firstName: String {get set} var lastName: String {get set} func getFullName() -> String }
The FullName protocol now requires one method named getFullName() and two read- write properties named firstName and lastName.
For value types, such as the structure, if we intend for a method to modify the instances that it belongs to, we must prefix the method definition with the mutating keyword. This keyword indicates that the method is allowed to modify the instance it belongs to. The following example shows how to use the mutating keyword with a method definition:
mutating func changeName()
If we mark a method requirement as mutating, we don't need to write the mutating keyword for that method when we adopt the protocol with a reference (class) type. The mutating keyword is only used with value (structures or enumerations) types.
Optional requirements
There are times when we want protocols to define optional requirements. An optional requirement is a method or property that doesn't need to be implemented. To use optional requirements, we need to start off by marking the protocol with the @objc attribute.
To mark a property or method as optional, we use the optional keyword. The following example shows how we would create both an optional property and also an optional method:
@objc protocol Phone { var phoneNumber: String {get set} @objc optional var emailAddress: String {get set} func dialNumber() @objc optional func getEmail() }
If we are using the @objc attribute, as shown in the previous example, we cannot use the mutating keyword because it isn't valid for classes. Now, let's explore how protocol inheritance works.
Protocol composition
Protocol composition lets our types adopt multiple protocols. This is a major advantage that we get when we use protocols rather than a class hierarchy because classes, in Swift and other single-inheritance languages, can only inherit from one superclass. The syntax for protocol composition is the same as the syntax for protocol inheritance that we just saw. The following example shows how we would use protocol composition:
struct MyStruct: ProtocolOne, ProtocolTwo, Protocolthree { //implementation here }
Protocol composition allows us to break our requirements into many smaller components rather than inheriting all the requirements from a single protocol or single superclass. This allows our type families to grow in width rather than height, which means we avoid creating bloated types that contain requirements that are not needed by all conforming types. Protocol composition may seem like a very simple concept, but it is a concept that is essential to protocol-oriented programming. Let's look at an example of protocol composition so that we can see the advantage we get from using it.
Let's say that we have the class hierarchy that's shown in the following diagram:
In this class hierarchy, we have a base class named Athlete. The Athlete base class then has two subclasses named Amateur and Pro. These classes are used depending on whether the athlete is an amateur athlete or a pro athlete. An amateur athlete may be a collegiate athlete, and we would need to store information such as which school they go to and their GPA. A pro athlete is one that gets paid for playing the game. For the pro athletes, we would need to store information such as what team they play for and their salary.
In this example, things get a little messy under the Amateur and Pro classes. As we can see, we have separate football player classes under both the Amateur and Pro classes (the AmFootballPlayer and ProFootballPlayer classes). We also have separate baseball classes under both the Amateur and Pro classes (the AmBaseballPlayer and ProBaseballPlayer classes). This means we need to have a lot of duplicate code between these classes.
With protocol composition, instead of having a class hierarchy where our subclasses inherit all the functionality from a single superclass, we have a collection of protocols that we can mix and match in our types:
We can then use one or more of these protocols as needed for our types. For example, we can create an AmFootballPlayer structure that conforms to the Athlete, Amateur, and FootballPlayer protocols. We could then create the ProFootballPlayer structure that conforms to the Athlete, Pro, and FootballPlayer protocols. This allows us to be very specific about the requirements for our types and only adopt the requirements that we need.
From a pure protocol point of view, this example may not make a lot of sense right now because protocols only define the requirements; however, in Chapter 3, Extensions, we will look at how protocol extensions can be used to implement these types with minimal duplicate code.
Now, let's look at how a protocol is a full-fledged type in Swift.
