Book Image

Functional Kotlin

Book Image

Functional Kotlin

Overview of this book

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.
Table of Contents (22 chapters)
Title Page
Copyright and Credits
Packt Upsell

Managing mutable state

The main concern (and nightmare fuel) when we deal with asynchronous code is how to handle mutable state. We covered how to reduce mutable state with a functional style in Chapter 3, Immutability - It's Important. But sometimes it is impossible to use a functional immutable style. Coroutines offer some alternatives to this problem.

In the following example, we'll use several coroutines to update a counter:

import kotlin.system.measureTimeMillis

suspend fun repeatInParallel(times: Int, block: suspend () -> Unit) {
   val job = launch {
      repeat(times) {
         launch(coroutineContext) {

fun main(args: Array<String>) = runBlocking {
   var counter = 0

   val time = measureTimeMillis {
      repeatInParallel(1_000_000) {
   println("counter = $counter")
   println("time = $time")

On smaller numbers, counter is right, but once we start increasing the size, we'll...