Book Image

Hands-On Design Patterns with Kotlin

By : Alexey Soshin
Book Image

Hands-On Design Patterns with Kotlin

By: Alexey Soshin

Overview of this book

Design patterns enable you as a developer to speed up the development process by providing you with proven development paradigms. Reusing design patterns helps prevent complex issues that can cause major problems, improves your code base, promotes code reuse, and makes an architecture more robust. The mission of this book is to ease the adoption of design patterns in Kotlin and provide good practices for programmers. The book begins by showing you the practical aspects of smarter coding in Kotlin, explaining the basic Kotlin syntax and the impact of design patterns. From there, the book provides an in-depth explanation of the classical design patterns of creational, structural, and behavioral families, before heading into functional programming. It then takes you through reactive and concurrent patterns, teaching you about using streams, threads, and coroutines to write better code along the way By the end of the book, you will be able to efficiently address common problems faced while developing applications and be comfortable working on scalable and maintainable projects of any size.
Table of Contents (13 chapters)

Recursion

Recursion is a function invoking itself with new arguments:

fun sumRec(i: Int, numbers: List<Int>): Long {
return if (i == numbers.size) {
0
} else {
numbers[i] + sumRec(i + 1, numbers)
}
}

We usually avoid recursion, due to Stack Overflow error that we may receive if our call stack is too deep. You can call this function with a list that contains a million numbers to experience it:

val numbers = List(1_000_000) {it}
println(sumRec(0, numbers)) // Crashed pretty soon, around 7K

One of the great benefits of tail recursion is that it avoids the dreaded stack overflow exception.

Let's rewrite our recursive function using a new keyword, tailrec, to avoid that problem:

tailrec fun sumRec(i: Int, sum: Long, numbers: List<Int>): Long {
return if (i == numbers.size) {
return sum
} else {
sumRec(i+1, numbers[i] + sum...