Book Image

Android Development with Kotlin

By : Igor Wojda, Marcin Moskala
Book Image

Android Development with Kotlin

By: Igor Wojda, Marcin Moskala

Overview of this book

Nowadays, improved application development does not just mean building better performing applications. It has become crucial to find improved ways of writing code. Kotlin is a language that helps developers build amazing Android applications easily and effectively. This book discusses Kotlin features in context of Android development. It demonstrates how common examples that are typical for Android development, can be simplified using Kotlin. It also shows all the benefits, improvements and new possibilities provided by this language. The book is divided in three modules that show the power of Kotlin and teach you how to use it properly. Each module present features in different levels of advancement. The first module covers Kotlin basics. This module will lay a firm foundation for the rest of the chapters so you are able to read and understand most of the Kotlin code. The next module dives deeper into the building blocks of Kotlin, such as functions, classes, and function types. You will learn how Kotlin brings many improvements to the table by improving common Java concepts and decreasing code verbosity. The last module presents features that are not present in Java. You will learn how certain tasks can be achieved in simpler ways thanks to Kotlin. Through the book, you will learn how to use Kotlin for Android development. You will get to know and understand most important Kotlin features, and how they can be used. You will be ready to start your own adventure with Android development with Kotlin.
Table of Contents (16 chapters)
Title Page
About the Authors
About the Reviewers
Customer Feedback
Making Your Marvel Gallery Application

Underscore for unused variables

In some cases, we define a lambda expression that does not use all its parameters. When we leave them named, they might be distracting to a programmer who is reading the lambda expression and trying to understand its purpose. Let's look at the function that filters every second element. The second parameter is the element value, and it is unused in this example:

    list.filterIndexed { index, value -> index % 2 == 0 } 

To prevent a misunderstanding, there are some conventions used, such as ignoring the parameter names:

    list.filterIndexed { index, ignored -> index % 2 == 0 } 

Because these conventions were unclear and problematic, Kotlin introduced underscore notation, which is used as a replacement for the names of parameters that are not used:

    list.filterIndexed { index, _ -> index % 2 == 0 } 

This notation is suggested, and there is a warning displayed when a lambda expression parameter is unused: