Book Image

Kotlin Design Patterns and Best Practices - Second Edition

By : Alexey Soshin
Book Image

Kotlin Design Patterns and Best Practices - Second Edition

By: Alexey Soshin

Overview of this book

This book shows you how easy it can be to implement traditional design patterns in the modern multi-paradigm Kotlin programming language, and takes you through the new patterns and paradigms that have emerged. This second edition is updated to cover the changes introduced from Kotlin 1.2 up to 1.5 and focuses more on the idiomatic usage of coroutines, which have become a stable language feature. You'll begin by learning about the practical aspects of smarter coding in Kotlin, as well as understanding basic Kotlin syntax and the impact of design patterns on your code. The book also provides an in-depth explanation of the classical design patterns, such as Creational, Structural, and Behavioral families, before moving on to functional programming. You'll go through reactive and concurrent patterns, and finally, get to grips with coroutines and structured concurrency to write performant, extensible, and maintainable code. By the end of this Kotlin book, you'll have explored the latest trends in architecture and design patterns for microservices. You’ll also understand the tradeoffs when choosing between different architectures and make informed decisions.
Table of Contents (17 chapters)
1
Section 1: Classical Patterns
6
Section 2: Reactive and Concurrent Patterns
11
Section 3: Practical Application of Design Patterns

Implementing Algebraic Data Types

Algebraic Data Types, or ATDs for short, is a concept from functional programming and is very similar to the Composite design pattern we discussed in Chapter 3, Understanding Structural Patterns.

To understand how ADTs work and what their benefits are, let's discuss how we can implement a simple binary tree in Kotlin.

First, let's declare an interface for our tree. Since a tree data structure can contain any type of data, we can parameterize it with a type (T):

sealed interface Tree<out T>

The type is marked with an out keyword, which means that this type is covariant. If you aren't familiar with this term, we'll cover it later, while implementing the interface.

The opposite of a covariant is a contravariant. Contravariant types should be marked using the in keyword.

We can also mark this interface with a sealed keyword. We saw this keyword applied to regular classes in Chapter 4, Getting Familiar with Behavioral...