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Functional Kotlin E-Book

Mario Arias

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Herausgeber: Packt Publishing
Kategorie: Wissenschaft und neue Technologien
Sprache: Englisch

Beschreibung

Learn how to apply Functional Programming with Kotlin to real-life projects with popular libraries like Arrow.

Key Features

~Focus on the functional aspects of Kotlin and identify the advantages that functional programming brings to the table and the associated coding benefits,~Implement common functional programming design patterns and techniques. ~Learn to combine OOP and Reactive Programming with Functional Programming and how RxKotlin and funkTionale can help you implementing Functional Programming in Kotlin

Book Description

Functional programming makes your application faster, improves performance, and increases your productivity. Kotlin supports many of the popular and advanced functional features of functional languages. This book will cover the A-Z of functional programming in Kotlin. This book bridges the language gap for Kotlin developers by showing you how to create and consume functional constructs in Kotlin. We also bridge the domain gap by showing how functional constructs can be applied in business scenarios. We’ll take you through lambdas, pattern matching, immutability, and help you develop a deep understanding of the concepts and practices of functional programming. If you want learn to address problems using Recursion, Koltin has support for it as well. You’ll also learn how to use the funKtionale library to perform currying and lazy programming and more. Finally, you’ll learn functional design patterns and techniques that will make you a better programmer.By the end of the book, you will be more confident in your functional programming skills and will be able to apply them while programming in Kotlin.

What you will learn

Learn the Concepts of Functional Programming with Kotlin
Discover the Coroutines in Kotlin
Uncover Using funkTionale plugin
Learn Monads, Functiors and Applicatives
Combine Functional Programming with OOP and Reactive Programming
Uncover Using Monads with funkTionale
Discover Stream Processing

Who this book is for

Kotlin developers who have no functional programming experience, will benefit from this book.

Mario Arias is a software engineer and Spring certified instructor with more than 12 years of experience in software development and design, databases, training material design, and training delivery. He currently works as a software engineer in Manchester, UK, for Cake Solutions Ltd., a BAMTECH media company. Mario is well-known member of the Kotlin community and is part of the Arrow team, the group that developed and maintains the Arrow functional library. In his free time, he rides his bicycle and trains Brazilian Jiu-Jitsu. Rivu Chakraborty is a Caster.io instructor, Google Certified Android Developer, and senior tech member of Institute of Engineers (India). With more than 5 years of experience, he is currently working as a senior software engineer (Android) at Indus Net Technologies Pvt.Ltd. Rivu is a Kotlin and Android enthusiast and a Kotlin evangelist. He has been using Kotlin for more than 2 years. Rivu is the founder organizer of Kotlin Kolkata UG. He is also a core organizing team member of GDG Kolkata. Rivu has previously authored, Reactive Programming in Kotlin, and is working on two more books on Kotlin.

Details

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Seitenzahl: 353

Veröffentlichungsjahr: 2018

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Leseprobe

Functional Kotlin

Extend your OOP skills and implement functional techniques in Kotlin and Arrow

Mario Arias

Rivu Chakraborty

BIRMINGHAM - MUMBAI

Functional Kotlin

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the authors, nor Packt Publishing or its dealers and distributors, will be held liable for any damages caused or alleged to have been caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

Commissioning Editor: Aaron LazarAcquisition Editor: Sandeep MishraContent Development Editor: Zeeyan PinheiroTechnical Editor: Ruvika RaoCopy Editor: Safis EditingProject Coordinator: Vaidehi SawantProofreader: Safis EditingIndexer: Tejas Daruwale SoniGraphics: Jason MonteiroProduction Coordinator: Arvindkumar Gupta

First published: February 2018

Production reference: 1220218

Published by Packt Publishing Ltd. Livery Place 35 Livery Street Birmingham B3 2PB, UK.

ISBN 978-1-78847-648-5

www.packtpub.com

To my parents; my wife, Esha; and our newborn son, Rishaan.

– Rivu Chakraborty

To Ari, see you soon, and to my Dad, see you in heaven.

– Mario Arias

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Contributors

About the authors

Mario is well-known member of the Kotlin community and is part of the Arrow team, the group that developed and maintains the Arrow functional library. In his free time, he rides his bicycle and trains Brazilian Jiu-Jitsu.

My first and the most important acknowledgement is to my Lord and Saviour, Jesus Christ. Thanks to my soon-to-be wife, Ari, for her continuous support and patience. To my family and friends. Thanks to the JetBrains team for creating a fantastic language, my teammates at Arrow, to my co-author, Rivu Chakraborty, and the entire team at Packt.

Rivu Chakraborty is a Caster.io instructor, Google Certified Android Developer, and senior tech member of Institute of Engineers (India). With more than 5 years of experience, he is currently working as a senior software engineer (Android) at Indus Net Technologies Pvt. Ltd.

Rivu is a Kotlin and Android enthusiast and a Kotlin evangelist. He has been using Kotlin for more than 2 years. Rivu is the founder organizer of Kotlin Kolkata UG. He is also a core organizing team member of GDG Kolkata. Rivu has previously authored, Reactive Programming in Kotlin, and is working on two more books on Kotlin.

Thanks to my parents; my wife, Esha; and my son, Rishaan; for having my back and trusting me. Thanks to the Kotlin Kolkata community for inspiring me to write books and sharing my knowledge. Thanks to the reviewers of this book for their valuable feedback and inputs. Thanks a lot to my co-author, Mario Arias, for writing this book with me. I've learned a lot from him.

About the reviewer

Ganesh Samarthyam is a co-founder of CodeOps Technologies, a software technology, consultancy, and training company based in Bangalore. He has 16 years of experience in the IT industry, and his latest book, Refactoring for Software Design Smells: Managing Technical Debt by Morgan Kaufmann/Elsevier, has been translated to languages like Korean and Chinese. Ganesh loves exploring anything and everything about technology in his free time.

Packt is searching for authors like you

If you're interested in becoming an author for Packt, please visit authors.packtpub.com and apply today. We have worked with thousands of developers and tech professionals, just like you, to help them share their insight with the global tech community. You can make a general application, apply for a specific hot topic that we are recruiting an author for, or submit your own idea.

Title Page

Functional Kotlin

Dedication

Packt Upsell

Why subscribe?

PacktPub.com

Contributors

About the authors

About the reviewer

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

Download the color images

Conventions used

Get in touch

Reviews

Kotlin – Data Types, Objects, and Classes

Classes

Properties

Methods

Inheritance

Abstract classes

Interfaces

Objects

Object declarations

Companion objects

Generics

Type alias

Nullable types

Checking for null

Checking for non-null types

Safe calls

The Elvis (?:) operator

The (!!) operator

Kotlin's type system

The Any type

Minimum common types

The Unit type

The Nothing type

Other types

Data classes

Canonical methods

The copy() method

Destructuring methods

Annotations

Enum

Summary

Getting Started with Functional Programming

What is functional programming?

Basics concepts

First-class and higher-order functions

Pure functions

Recursive functions

Lazy evaluation

Functional collections

Implementing a functional list

Summary

Immutability - It's Important

What is immutability?

Implementing immutability in Kotlin

The difference between var and val

Compile time constants

Types of immutability

Immutable reference  (referential immutability)

Immutable values

Immutable collections

The advantages of immutability

Thread safety

Low coupling

Referential transparency

Failure atomicity

Caching

Compiler optimization

Pure functions

The disadvantages of immutability

Summary

Functions, Function Types, and Side Effects

Functions in Kotlin

Returning two values from a function

Extension functions

Default arguments

Nested functions

Function types in functional programming

Lambda

Function as property

High order functions

Pure functions and side effects

Side effects

Pure functions

Summary

Preface

With Google's announcement at the I/O Conference in 2017 to make Kotlin an official language for Android, Kotlin has been gaining popularity among developers around the world.

However, Kotlin's use and popularity aren't limited to the Android community. Many other communities, such as the desktop, web, and backend community are embracing Kotlin too. Many new libraries and frameworks are being created and existing ones are providing support for Kotlin.

With more developers coming to the Kotlin community and with its natural flexibility, more programming styles are being tried. The purpose of this book is to introduce the functional programming style to the wide Kotlin community, leading and guiding on the first steps, and giving the basic tools to progress further to more advanced concepts.

Who this book is for

This book is for Kotlin users (programmers, engineers, library authors, and architects) who have a basic understanding of Kotlin and want to understand the basics ideas behind functional programming and how to use it in a practical way (if you're entirely new to Kotlin, our Appendix, Kotlin's Quick Start will give you a quick start with the language).

What this book covers

Chapter 1, Kotlin - Data Types, Objects, and Classes, introduces you to object-oriented programming in Kotlin. Kotlin is primary object-oriented programming, and we'll use these features to introduce a functional programming style.

Chapter 2, Getting Started with Functional Programming, covers the basic principles of functional programming using Kotlin's object-oriented programming features.

Chapter 3, Immutability - It's Important, emphasizes on immutability as one of the most important concepts in functional programming. This chapter will give you an in-depth understanding of immutability.

Chapter 4, Functions, Function Types, and Side Effects, introduces you to the basic functional programming concepts around functions, pure functions, and various function types and side effects.

Chapter 5, More on Functions, talks about Kotlin's features for functional programming such as extension functions, operator overloading, DSLs, and corecursion.

Chapter 6, Delegates in Kotlin, covers how Kotlin has language-level support for delegates. Though delegates are a object-oriented programming concept, they can be helpful in making your code more modular.

Chapter 7, Asynchronous Programming with Coroutines, gives you an introduction to asynchronous programming in Kotlin, comparing different styles against coroutines.

Chapter 8, Collections and Data Operations in Kotlin, covers the enhanced collections API by Kotlin and the functional interfaces that Kotlin's collections framework has to offer.

Chapter 9, Functional Programming and Reactive Programming, shows how functional programming can be combined with other programming paradigms to get the best out of them. This chapter discusses how you can combine functional programming with object-oriented programming and reactive programming.

Chapter 10, Functors, Applicatives and Monads, gives you an introduction to typed functional programming and its basic concepts. It also talks about how to implement it in Kotlin.

Chapter 11, Working with Streams in Kotlin, gets you introduced to the Streams API in Kotlin.

Chapter 12, Getting Started with Arrow, covers how to use Arrow and its extensions for functional programming, function composition, currying, partial application, memoization, and optics.

Chapter 13, Arrow Types, helps you understand Arrow data types such as Option, Either, Try, and State and its type classes, functors, and monads.

Appendix, Kotlin's Quick Start, it provides everything that you need to start writing a Kotlin code, such as tools, basic syntax constructs and other resources to help you progress in your Kotlin journey.

To get the most out of this book

The only recommended software to run and write Kotlin programs is IntelliJ IDEA (there are other ways to do it, and we cover them in the Appendix, Kotlin's Quick Start).

You can download IntelliJ IDEA from https://www.jetbrains.com/idea/download/.

You can install IntelliJ IDEA on Windows, Mac, and Linux:

For Windows

: You can use any Windows version from XP to 10. To install it on Windows, run the installer executable and follow the instructions.

For Mac

: You can use any macOS version starting from 10.8. To install it on macOS, mount the disk image file and copy

IntelliJ IDEA.app

to your

Application

folder.

For Linux

: You can use any GNOME or KDE desktop. To install it Linux unpack the

tar.gz

file using the

tar -xzf idea-*.tar.gz

command and run the

idea.sh

from the

bin

subdirectory.

Download the example code files

You can download the example code files for this book from your account at www.packtpub.com. If you purchased this book elsewhere, you can visit www.packtpub.com/support and register to have the files emailed directly to you.

You can download the code files by following these steps:

www.packtpub.com

Select the

SUPPORT

tab.

Click on

Code Downloads & Errata

Enter the name of the book in the

box and follow the onscreen instructions.

Once the file is downloaded, please make sure that you unzip or extract the folder using the latest version of:

WinRAR/7-Zip for Windows

Zipeg/iZip/UnRarX for Mac

7-Zip/PeaZip for Linux

The code bundle for the book is also hosted on GitHub at https://github.com/PacktPublishing/Functional-Kotlin. 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 athttps://github.com/PacktPublishing/. Check them out!

Download the color images

We also provide a PDF file that has color images of the screenshots/diagrams used in this book. You can download it here: https://www.packtpub.com/sites/default/files/downloads/FunctionalKotlin_ColorImages.pdf .

Get in touch

Feedback from our readers is always welcome.

General feedback: Email [email protected] and mention the book title in the subject of your message. If you have questions about any aspect of this book, please email us at [email protected].

Errata: Although we have taken every care to ensure the accuracy of our content, mistakes do happen. If you have found a mistake in this book, we would be grateful if you would report this to us. Please visit www.packtpub.com/submit-errata, selecting your book, clicking on the Errata Submission Form link, and entering the details.

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Reviews

Please leave a review. Once you have read and used this book, why not leave a review on the site that you purchased it from? Potential readers can then see and use your unbiased opinion to make purchase decisions, we at Packt can understand what you think about our products, and our authors can see your feedback on their book. Thank you!

For more information about Packt, please visit packtpub.com

Kotlin – Data Types, Objects, and Classes

In this chapter, we'll cover Kotlin's type system, object-oriented programming (OOP) with Kotlin, modifiers, destructuring declarations, and more.

Kotlin is, primarily, an OOP language with some functional features. When we use OOP languages to resolve problems, we try to model the objects that are a part of our problem in an abstract way with the information that is relevant to the problem.

If we're designing an HR module for our company, we'll model employees with state or data (name, date of birth, social security number, and others) and behavior (pay salary, transfer to another division, and others). Because a person can be very complex, there is information that isn't relevant for our problem or domain. For example, the employee's favorite style of bicycle isn't relevant for our HR system, but it is very relevant for an online cycling shop.

Once we identify the objects (with data and behavior) and the relationship with other objects of our domain, we can start developing and writing the code that we'll make a part of our software solution. We'll use language constructs (construct is a fancy way to say allowed syntax) to write the objects, categories, relationships, and so on.

Kotlin has many constructs that we can use to write our programs and, in this chapter, we'll cover many of those constructs, such as:

Classes

Inheritance

Abstract classes

Interfaces

Objects

Generics

Type alias

Null types

Kotlin's type system

Other types

Generics

This section is just a short introduction to generics; later, we'll cover it in detail.

Generic programming is a style programming that focuses on creating algorithms (and collaterally, data structures) that work on general problems.

The Kotlin way to support generic programming is using type parameters. In a few words, we wrote our code with type parameters and, later on, we pass those types as parameters when we use them.

Let's take, for example, our Oven interface:

interface Oven { fun process(product: Bakeable)}

An oven is a machine, so we could generalize it more:

interface Machine<T> { fun process(product: T)}

The Machine<T> interface defines a type parameter T and a method process(T).

Now, we can extend it with Oven:

interface Oven: Machine<Bakeable>

Now, Oven is extending Machine with the Bakeable type parameter, so the process method now takes Bakeable as a parameter.