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 null object design pattern

Most object-oriented languages have a way of specifying the nonexistence of some value. In Scala and Java, for example, this could be the null value that can be assigned to an object. Calling any method on an object that is null would result in a NullPointerException, hence developers should be careful and check whether there is such a possibility. These checks, however, could make the source code hard to follow and extend as developers should always be aware. This is where the null object design pattern is helpful. Its purpose is:

Note

To define an actual object that represents the null value and has neutral behavior.

Using null objects removes the need to check whether something is set to null or not. The code becomes much more readable and easy to understand and makes bug occurrence harder.

Class diagram

For the class diagram, let's imagine that we have a system that has to poll a queue for messages. Of course, this queue might not always have anything to offer...

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