Book Image

Kotlin Programming Cookbook

By : Aanand Shekhar Roy, Rashi Karanpuria
Book Image

Kotlin Programming Cookbook

By: Aanand Shekhar Roy, Rashi Karanpuria

Overview of this book

The Android team has announced first-class support for Kotlin 1.1. This acts as an added boost to the language and more and more developers are now looking at Kotlin for their application development. This recipe-based book will be your guide to learning the Kotlin programming language. The recipes in this book build from simple language concepts to more complex applications of the language. After the fundamentals of the language, you will learn how to apply the object-oriented programming features of Kotlin 1.1. Programming with Lambdas will show you how to use the functional power of Kotlin. This book has recipes that will get you started with Android programming with Kotlin 1.1, providing quick solutions to common problems encountered during Android app development. You will also be taken through recipes that will teach you microservice and concurrent programming with Kotlin. Going forward, you will learn to test and secure your applications with Kotlin. Finally, this book supplies recipes that will help you migrate your Java code to Kotlin and will help ensure that it's interoperable with Java.
Table of Contents (21 chapters)
Title Page
Copyright and Credits
Packt Upsell

Writing your own delegates

Delegated properties are one of the best features of Kotlin language. We have already seen observable and vetoable delegates. In this recipe, we will learn how to create our own custom delegate. As a demo example, we will create a delegate property that can only be initialized once; if done again, it should throw an exception. So let's dive into it and see how we can achieve it.

Getting ready

We will be using IntelliJ IDEA for coding purposes. You can use any IDE capable of executing Kotlin code.

How to do it…

Now, let's dive in and learn how to create our own delegates:

  1. Let's create a custom delegate named as  SingleInitializationProperty. This custom delegate property will throw an exception if the variable isn't initialized, and it can only be initialized once. Doing it a second time will throw an exception. Let's take a look at our custom delegate class:
class SingleInitializableProperty<T>() : ReadWriteProperty<Any?, T>{
    private var value: T? = null...