Preface

Design patterns represent a compendium of best practices and replicable solutions for frequently encountered software development challenges. These patterns, forged through the collective experience of seasoned developers, offer proven solutions for specific, recurring issues in software design, adaptable to a range of situations. They furnish developers with a shared vocabulary to facilitate communication, collaboration, and code maintenance. Fundamentally, design patterns empower developers to write superior, more efficient, and maintainable code by diminishing the time spent devising solutions for common problems from the ground up.

Kotlin is a versatile programming language that embraces multiple programming paradigms and was crafted by JetBrains, who are renowned for creating widely-used integrated development environments, including IntelliJ IDEA.

The primary goal of this book is to introduce you to classical design patterns, whether you’re unfamiliar with them entirely or are seeking to implement them in Kotlin after using them with other languages. Kotlin, a contemporary language, naturally integrates many essential design patterns within its own syntax and core libraries, often eliminating the need to implement these patterns manually. Nonetheless, recognizing the design patterns embodied by specific language features remains valuable.

This updated edition focuses on the advancements in Kotlin up to Kotlin 2.0. With the ongoing evolution of the Kotlin ecosystem, this edition highlights some of the most thrilling features, such as context receivers, and significant libraries like Arrow, justifying the need for this new edition.

Who this book is for

This book is intended for developers who want to utilize design patterns they’ve learned from other programming languages in Kotlin to create robust, scalable, and easily maintainable applications.

What this book covers

Chapter 1, Getting Started with Kotlin, introduces you to the basic syntax of Kotlin and explain how design patterns can be applied effectively in Kotlin. The focus is not to cover the entire language vocabulary, but rather to provide a clear understanding of the fundamental concepts and idioms. Subsequent chapters will gradually introduce additional language features that are relevant to the design patterns being discussed. By the end of this chapter, you’ll have a strong foundation in the language and be ready to explore more advanced topics.

Chapter 2, Working with Creational Patterns, teaches you about classical creational patterns that are already embedded in the Kotlin language, as well as how to implement those that are not. These patterns focus on how and when to create objects. By mastering these patterns you will be able to manage your objects more effectively, adapt well to changes, and write more maintainable code. The chapter covers various patterns, including Singleton and Builder.

Chapter 3, Understanding Structural Patterns, introduces classical structural design patterns that can be used to extend the functionality of objects and adapt them to changes. By learning these patterns you will be able to write more robust and adaptable code. The chapter covers several patterns, including the widely used Decorator and Adapter patterns, which are essential for achieving greater flexibility and maintainability in software development.

Chapter 4, Getting Familiar with Behavioral Patterns, focuses on behavioral patterns in Kotlin, which deal with how objects interact with each other. You will learn how an object can exhibit different behaviors depending on the situation, how objects can communicate without direct knowledge of one another, and how to iterate over complex structures easily. By understanding these patterns you can write more flexible and reusable code that is easier to maintain over time.

Chapter 5, Introducing Functional Programming, this chapter presents the fundamental principles of functional programming and their connection to Kotlin. Without delving into much new syntax, we will address key concepts like data immutability and treating functions as first-class values. While these principles were crucial for grasping Kotlin’s advantages in the earlier chapters, here, we examine their significance within the realm of functional programming. Instead of examining their application in implementing design patterns, our focus will be on their essential role in crafting code that is more concise, modular, and maintainable.

Chapter 6, Threads and Coroutines, centers on efficiently managing a multitude of requests in our application. Threads are traditionally the go-to for concurrency in contemporary applications; however, Kotlin offers coroutines as a superior, more efficient option.

We’ll examine the advantages of utilizing coroutines and demonstrate their implementation for processing a high rate of requests. Furthermore, we will explore structured concurrency in Kotlin, a feature that enhances the safety and efficiency of concurrent code. A comprehensive explanation of this concept will be provided, along with insights into its application for boosting the performance of our applications.

Chapter 7, Controlling the Data Flow, covers higher-order functions that can be used with collections and concurrent data structures. We’ll also introduce Channels and Flows, which provide concurrent and reactive solutions that leverage these higher-order functions.

Chapter 8, Designing for Concurrency, explores the most widely utilized concurrency design patterns, particularly those implemented using coroutines. These patterns enable the simultaneous management of multiple tasks. We will also discuss how coroutines synchronize their execution to avert race conditions and guarantee thread safety.

Chapter 9, Idioms and Anti-patterns, is dedicated to discussing the optimal and less optimal practices of coding in Kotlin. We’ll go over what the preferred coding style for Kotlin is and identify certain coding patterns that are not recommended. Once you have completed this chapter, you should be able to produce Kotlin code that is easier to read and maintain, as well as steer clear of typical coding mistakes.

Chapter 10, Practical Functional Programming with Arrow, leverages our knowledge of Functional Programming and Coroutines from the previous parts and puts it into action using the Arrow framework. Arrow aims to provide a uniform and idiomatic functional programming experience for Kotlin developers, making it accessible to all. We’ll explore the power of Arrow in writing concise, expressive, and maintainable code. Throughout this chapter, we’ll highlight the key features and benefits of the Arrow framework, showcasing how it enhances development and enables the adoption of functional programming principles in Kotlin. With Arrow, developers can unlock the full potential of functional programming while capitalizing on the flexibility and robustness of Kotlin.

Chapter 11, Concurrent Microservices with Ktor, demonstrates how to put the knowledge learned in previous chapters into practice by building a microservice using Kotlin. We will use the Ktor framework, developed by Jetbrains, the creators of the Kotlin programming language. By following the examples in this chapter, you will be able to create your own microservices using Kotlin and Ktor.

Chapter 12, Reactive Microservices with Vert.x, explores an alternative method for building microservices with Kotlin by utilizing the Vert.x framework. Vert.x is based on reactive design patterns. We will examine the advantages and disadvantages of each approach and analyze real code examples to determine when to use each one.

Assessments, gives you the answers to the questions that follow each chapter throughout the rest of the book.

To get the most out of this book

Before you dive into this book, it’s important to have a solid understanding of at least one programming language. Knowledge of classical design patterns in your language of choice will be beneficial. Although the book is comprehensible to programmers versed in different languages, some familiarity with Java would be an added advantage.

Download the example code files

The code bundle for the book is hosted on GitHub at https://github.com/PacktPublishing/Kotlin-Design-Patterns-and-Best-Practices_Third-Edition. 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. For example; “The let() function is useful for operating on nullable objects, executing code only if the object is non-null.”

A block of code is set as follows:

val clintEastwoodQuotes = mapOf(
    "The Good, The Bad, The Ugly" to "Every gun makes its own tune.",
    "A Fistful Of Dollars" to "My mistake: four coffins."
)

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

data class JamesBondMovie(
    var actorName: String = "Sean Connery",
    var movieName: String = "From Russia with Love"
)

Any command-line input or output is written as follows:

> Node(value=1, left=Empty, right=Node(value=2, left=Node(value=3, left=Empty, right=Empty), right=Empty))

Bold: Indicates a new term, an important word, or words that you see on the screen. For instance, words in menus or dialog boxes appear in the text like this. For example: “The State pattern extends this idea by allowing objects to transition seamlessly between various states.”

Warnings or important notes appear like this.

Tips and tricks appear like this.

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