Practical Object-Oriented Design

The Complete Guide to Writing Maintainable, Manageable, Pleasing, and Powerful Object-Oriented Applications

Object-oriented programming languages exist to help you create beautiful, straightforward applications that are easy to change and simple to extend. Unfortunately, the world is awash with object-oriented (OO) applications that are difficult to understand and expensive to change. Practical Object-Oriented Design, Second Edition, immerses you in an OO mindset and teaches you powerful, real-world, object-oriented design techniques with simple and practical examples.

Sandi Metz demonstrates how to build new applications that can “survive success” and repair existing applications that have become impossible to change. Each technique is illustrated with extended examples in the easy-to-understand Ruby programming language, all downloadable from the companion website, poodr.com. Fully updated for Ruby 2.5, this guide shows how to

• Decide what belongs in a single class
• Avoid entangling objects that should be kept separate
• Define flexible interfaces among objects
• Reduce programming overhead costs with duck typing
• Successfully apply inheritance
• Build objects via composition

Whatever your previous object-oriented experience, this concise guide will help you achieve the superior outcomes you’re looking for.

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Table of Contents

1 Object-Oriented Design

2 Designing Classes with a Single Responsibility

3 Managing Dependencies

4 Creating Flexible Interfaces

5 Reducing Costs with Duck Typing

6 Acquiring Behavior through Inheritance

7 Sharing Role Behavior with Modules

8 Combining Objects with Composition

9 Designing Cost-Effective Tests

About the Author

Sandi Metz is a programmer, teacher, author, and sometime consultant. In the past 30+ years she has written innumerable applications and creates practical solutions that produce working software that is easy to change. She has spoken about object-oriented design and refactoring at international Ruby conferences since 2009.