Book Image

Scala Functional Programming Patterns

By : Atul S. Khot
Book Image

Scala Functional Programming Patterns

By: Atul S. Khot

Overview of this book

Scala is used to construct elegant class hierarchies for maximum code reuse and extensibility and to implement their behavior using higher-order functions. Its functional programming (FP) features are a boon to help you design “easy to reason about” systems to control the growing software complexities. Knowing how and where to apply the many Scala techniques is challenging. Looking at Scala best practices in the context of what you already know helps you grasp these concepts quickly, and helps you see where and why to use them. This book begins with the rationale behind patterns to help you understand where and why each pattern is applied. You will discover what tail recursion brings to your table and will get an understanding of how to create solutions without mutations. We then explain the concept of memorization and infinite sequences for on-demand computation. Further, the book takes you through Scala’s stackable traits and dependency injection, a popular technique to produce loosely-coupled software systems. You will also explore how to currying favors to your code and how to simplify it by de-construction via pattern matching. We also show you how to do pipeline transformations using higher order functions such as the pipes and filters pattern. Then we guide you through the increasing importance of concurrent programming and the pitfalls of traditional code concurrency. Lastly, the book takes a paradigm shift to show you the different techniques that functional programming brings to your plate. This book is an invaluable source to help you understand and perform functional programming and solve common programming problems using Scala’s programming patterns.
Table of Contents (19 chapters)
Scala Functional Programming Patterns
Credits
About the Author
Aknowledgement
About the Reviewers
www.PacktPub.com
Preface
Index

Frills and thrills – the decorator pattern


We need to add the functionality whereby animals get inoculated by a vet. Also, an animal should be inoculated only once. In practice, we would normally inoculate them at intervals. However, we simplify things to make our point. We want to wrap the logic "if already inoculated, then skip" without touching the animal code. The decorator pattern now comes to our rescue.

A decorator is a design pattern that wraps an object. It mimics the interface of the object that it is decorating. Here is the Java code in which we will look at how Scala makes the pattern easy and breezy.

The Java listing here has just the necessary changes. Refer to the book source code for the complete listing:

public class AnimalDecorator extends Animal { // 1
  protected Animal animal; // 2
  public AnimalDecorator(Animal animal) {
    this.animal = animal;
  }
  public void getInoculated() {
    animal.getInoculated(); // 3 // delegate to next decorator
    // or animal
  }
  ...