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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
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
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
Chapter 3: Managing Dependencies 35
Understanding Dependencies 36
Writing Loosely Coupled Code 39
Managing Dependency Direction 51
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
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
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
Chapter 7: Sharing Role Behavior with Modules 141
Understanding Roles 142
Writing Inheritable Code 158
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
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