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

Partial functions

A partial function (not to be confused with partial applied function) is a function that is not defined for every possible value of its parameter type. In contrast, a total function is a function that is defined for every possible value.

Let's have a look at the following example:

fun main(args: Array<String>) {
   val upper: (String?) -> String = { s:String? -> s!!.toUpperCase()} //Partial function, it can't transform null

   listOf("one", "two", null, "four").map(upper).forEach(::println) //NPE

The upper function is a partial function; it can't process a null value despite the fact that null is a valid String? value. If you try to run this code, it will throw a NullPointerException (NPE).

Arrow provides an explicit type PartialFunction<T, R> for partial functions of type (T) -> R:

import arrow.core.PartialFunction

fun main(args: Array<String>) {
 val upper: (String?) -> String = { s: String? -> s!!.toUpperCase() } //Partial function, it...