Book Image

Scala Design Patterns

By : Ivan Nikolov
Book Image

Scala Design Patterns

By: Ivan Nikolov

Overview of this book

Scala has become increasingly popular in many different IT sectors. The language is exceptionally feature-rich which helps developers write less code and get faster results. Design patterns make developer’s lives easier by helping them write great software that is easy to maintain, runs efficiently and is valuable to the company or people concerned. You will learn about the various features of Scala and be able to apply well-known, industry-proven design patterns in your work. The book starts off by focusing on some of the most interesting features of Scala while using practical real-world examples. We will also cover the popular "Gang of Four" design patterns and show you how to incorporate functional patterns effectively. By the end of this book, you will have enough knowledge and understanding to quickly assess problems and come up with elegant solutions.

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Scala Design Patterns
Ivan Nikolov
Feb, 2016 | 382 pages
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Table of Contents (20 chapters)
Scala Design Patterns
Scala Design Patterns
Credits
Credits
About the Author
About the Author
Acknowledgments
Acknowledgments
About the Reviewer
About the Reviewer
www.PacktPub.com
www.PacktPub.com
Preface
Preface
Free Chapter
1
The Design Patterns Out There and Setting Up Your Environment
The Design Patterns Out There and Setting Up Your Environment
Design patterns
Design pattern categories
How to choose a design pattern
Setting up the development environment
Summary
2
Traits and Mixin Compositions
Traits and Mixin Compositions
Traits
Mixin compositions
Multiple inheritance
Linearization
Testing traits
Traits versus classes
Summary
3
Unification
Unification
Functions and classes
Algebraic data types and class hierarchies
Modules and objects
Summary
4
Abstract and Self Types
Abstract and Self Types
Abstract types
Polymorphism
Self types
Summary
5
Aspect-Oriented Programming and Components
Aspect-Oriented Programming and Components
Aspect-oriented programming
Chapter case example
Components in Scala
Summary
6
Creational Design Patterns
Creational Design Patterns
What are creational design patterns?
The factory method design pattern
The abstract factory
Other factory design patterns
Lazy initialization
The singleton design pattern
The builder design pattern
The prototype design pattern
Summary
7
Structural Design Patterns
Structural Design Patterns
What are structural design patterns?
The adapter design pattern
The decorator design pattern
The bridge design pattern
The composite design pattern
The facade design pattern
The flyweight design pattern
The proxy design pattern
Summary
8
Behavioral Design Patterns – Part 1
Behavioral Design Patterns – Part 1
What are behavioral design patterns?
The value object design pattern
The null object design pattern
The strategy design pattern
The command design pattern
The chain of responsibility design pattern
The interpreter design pattern
Summary
9
Behavioral Design Patterns – Part 2
Behavioral Design Patterns – Part 2
The iterator design pattern
The mediator design pattern
The memento design pattern
The observer design pattern
The state design pattern
The template method design pattern
The visitor design pattern
Summary
10
Functional Design Patterns – The Deep Theory
Functional Design Patterns – The Deep Theory
Abstraction and vocabulary
Monoids
Functors
Monads
Summary
11
Functional Design Patterns – Applying What We Learned
Functional Design Patterns – Applying What We Learned
The lens design pattern
The cake design pattern
The pimp my library design pattern
The stackable traits design pattern
The type class design pattern
Lazy evaluation
Partial functions
Implicit injection
Duck typing
Memoization
Summary
12
Real-Life Applications
Real-Life Applications
Why should we use libraries?
The Scalaz library
Writing a complete application
Summary
Index
Index

The singleton design pattern

The singleton design pattern ensures that a class has only one object instance in the entire application. It introduces a global state in the applications it is used in.

A singleton object can be initialized using different strategies—lazy initialization or eager initialization. This all depends on the intended use, the time it takes an object to be initialized, and so on.

Class diagram

Singletons are another example of design patterns, which are supported out of the box by the Scala programming language syntax. We achieve this using the object keyword. In this case, again, providing a class diagram is not necessary, so we will step right into the example in the next subsection.

Code example

The aim of this example is to show how to create singleton instances in Scala and have an understanding of when exactly instances are created in Scala. We will look at a class called StringUtils, which provides different utility methods related to strings:

object StringUtils {...
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