The Complete Guide to Writing More Maintainable, Manageable, Pleasing, and Powerful Ruby Applications   Ruby’s widely admired ease of use has a downside: Too many Ruby and Rails applications have been created without concern for their long-term maintenance or evolution. The Web is awash in Ruby code that is now virtually impossible to change or extend. This text helps you solve that problem by using powerful real-world object-oriented design techniques, which it thoroughly explains using simple and practical Ruby examples.   Sandi Metz has distilled a lifetime of conversations and presentations about object-oriented design into a set of Ruby-focused practices for crafting manageable, extensible, and pleasing code. She shows you 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, all downloadable from the companion Web site, poodr.info.   The first title to focus squarely on object-oriented Ruby application design, Practical Object-Oriented Design in Ruby will guide you to superior outcomes, whatever your previous Ruby experience. Novice Ruby programmers will find specific rules to live by; intermediate Ruby programmers will find valuable principles they can flexibly interpret and apply; and advanced Ruby programmers will find a common language they can use to lead development and guide their colleagues.   This guide will help you Understand how object-oriented programming can help you craft Ruby code that is easier to maintain and upgrade Decide what belongs in a single Ruby 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 Design cost-effective tests Solve common problems associated with poorly designed Ruby code  

Table of Contents:
Foreword         xv Introduction         xvii Acknowledgments         xxi About the Author         xxiii   Chapter 1: Object-Oriented Design         1 In Praise of Design   2 The Tools of Design   4 The Act of Design   7 A Brief Introduction to Object-Oriented Programming   11 Summary 14   Chapter 2: Designing Classes with a Single Responsibility         15 Deciding What Belongs in a Class   16 Grouping Methods into Classes   16 Organizing Code to Allow for Easy Changes   16 Creating Classes That Have a Single Responsibility   17 Writing Code That Embraces Change   24 Finally, the Real Wheel   33 Summary   34   Chapter 3: Managing Dependencies         35 Understanding Dependencies   36 Writing Loosely Coupled Code   39 Managing Dependency Direction   51 Summary   57   Chapter 4: Creating Flexible Interfaces         59 Understanding Interfaces   59 Defining Interfaces   61 Public Interfaces   62 Private Interfaces   62 Responsibilities, Dependencies, and Interfaces   62 Finding the Public Interface   63 Writing Code That Puts Its Best (Inter)Face Forward   76 The Law of Demeter   80 Summary   83   Chapter 5: Reducing Costs with Duck Typing         85 Understanding Duck Typing   85 Writing Code That Relies on Ducks   95 Conquering a Fear of Duck Typing   100 Summary   104   Chapter 6: Acquiring Behavior Through Inheritance         105 Understanding Classical Inheritance   105 Recognizing Where to Use Inheritance   106 Misapplying Inheritance   114 Finding the Abstraction   116 Managing Coupling Between Superclasses and Subclasses   129 Summary 139   Chapter 7: Sharing Role Behavior with Modules         141 Understanding Roles   142 Writing Inheritable Code   158 Summary   162   Chapter 8: Combining Objects with Composition         163 Composing a Bicycle of Parts   164 Composing the Parts Object   168 Manufacturing Parts   176 The Composed Bicycle   180 Deciding Between Inheritance and Composition   184 Summary   190   Chapter 9: Designing Cost-Effective Tests         191 Intentional Testing   192 Testing Incoming Messages   200 Testing Private Methods   213 Testing Outgoing Messages   215 Testing Duck Types   219 Testing Inherited Code   229 Summary 240   Afterword         241   Index          243