The Definitive Refactoring Guide, Fully Revamped for Ruby
With refactoring, programmers can transform even the most chaotic software into well-designed systems that are far easier to evolve and maintain. What’s more, they can do it one step at a time, through a series of simple, proven steps. Now, there’s an authoritative and extensively updated version of Martin Fowler’s classic refactoring book that utilizes Ruby examples and idioms throughout–not code adapted from Java or any other environment.
The authors introduce a detailed catalog of more than 70 proven Ruby refactorings, with specific guidance on when to apply each of them, step-by-step instructions for using them, and example code illustrating how they work. Many of the authors’ refactorings use powerful Ruby-specific features, and all code samples are available for download.
Leveraging Fowler’s original concepts, the authors show how to perform refactoring in a controlled, efficient, incremental manner, so you methodically improve your code’s structure without introducing new bugs. Whatever your role in writing or maintaining Ruby code, this book will be an indispensable resource.
This book will help you
• Understand the core principles of refactoring and the reasons for doing it
• Recognize “bad smells” in your Ruby code
• Rework bad designs into well-designed code, one step at a time
• Build tests to make sure your refactorings work properly
• Understand the challenges of refactoring and how they can be overcome
• Compose methods to package code properly
• Move features between objects to place responsibilities where they fit best
• Organize data to make it easier to work with
• Simplify conditional expressions and make more effective use of polymorphism
• Create interfaces that are easier to understand and use
• Generalize more effectively
• Perform larger refactorings that transform entire software systems and may take months or years
• Successfully refactor Ruby on Rails code
Table of Contents:
Foreword . . . xiii
Preface . . . xv
Acknowledgments . . . xx
About the Authors . . . xxii
Chapter 1: Refactoring, a First Example . . . 1
The Starting Point . . . 2
The First Step in Refactoring . . . 6
Decomposing and Redistributing the Statement Method . . . 7
Replacing the Conditional Logic on Price Code with Polymorphism . . . 32
Final Thoughts . . . 50
Chapter 2: Principles in Refactoring . . . 51
Where Did Refactoring Come From? . . . 51
Defining Refactoring . . . 52
Why Should You Refactor? . . . 54
When Should You Refactor? . . . 57
Why Refactoring Works . . . 60
What Do I Tell My Manager? . . . 61
Indirection and Refactoring . . . 61
Problems with Refactoring . . . 63
Refactoring and Design. . . . 67
It Takes A While to Create Nothing . . . 69
Refactoring and Performance . . . 70
Optimizing a Payroll System . . . 71
Chapter 3: Bad Smells in Code . . . 73
Duplicated Code . . . 74
Long Method . . . 74
Large Class . . . 76
Long Parameter List . . . 76
Divergent Change . . . 77
Shotgun Surgery . . . 78
Feature Envy . . . 78
Data Clumps . . . 79
Primitive Obsession . . . 79
Case Statements . . . 80
Parallel Inheritance Hierarchies . . . 81
Lazy Class . . . 81
Speculative Generality . . . 81
Temporary Field . . . 82
Message Chains . . . 82
Middle Man . . . 83
Inappropriate Intimacy . . . 83
Alternative Classes with Different Interfaces . . . 83
Incomplete Library Class . . . 84
Data Class . . . 84
Refused Bequest . . . 84
Comments . . . 85
Metaprogramming Madness . . . 86
Disjointed API . . . 86
Repetitive Boilerplate . . . 86
Chapter 4: Building Tests . . . 87
The Value of Self-Testing Code . . . 87
The Test::Unit Testing Framework . . . 88
Developer and Quality Assurance Tests . . . 91
Adding More Tests . . . 92
Chapter 5: Toward a Catalog of Refactorings . . . 97
Format of the Refactorings . . . 97
Finding References . . . 99
Chapter 6: Composing Methods . . . 101
Extract Method . . . 102
Inline Method . . . 108
Inline Temp . . . 110
Replace Temp with Query. . . 111
Replace Temp with Chain . . . 114
Introduce Explaining Variable . . . 117
Split Temporary Variable . . . 121
Remove Assignments to Parameters . . . 124
Replace Method with Method Object . . . 127
Substitute Algorithm . . . 131
Replace Loop with Collection Closure Method . . . 133
Extract Surrounding Method . . . 135
Introduce Class Annotation . . . 139
Introduce Named Parameter . . . 142
Remove Named Parameter . . . 147
Remove Unused Default Parameter . . . 150
Dynamic Method Definition . . . 152
Replace Dynamic Receptor with Dynamic Method Definition . . . 158
Isolate Dynamic Receptor . . . 160
Move Eval from Runtime to Parse Time . . . 165
Chapter 7: Moving Features Between Objects . . . 167
Move Method . . . 167
Move Field . . . 172
Extract Class . . . 175
Inline Class . . . 179
Hide Delegate . . . 181
Remove Middle Man . . . 185
Chapter 8: Organizing Data . . . 187
Self Encapsulate Field . . . 188
Replace Data Value with Object . . . 191
Change Value to Reference . . . 194
Change Reference to Value . . . 198
Replace Array with Object . . . 201
Replace Hash with Object . . . 206
Change Unidirectional Association to Bidirectional . . . 210
Change Bidirectional Association to Unidirectional . . . 213
Replace Magic Number with Symbolic Constant . . . 217
Encapsulate Collection . . . 219
Replace Record with Data Class . . . 224
Replace Type Code with Polymorphism . . . 225
Replace Type Code with Module Extension . . . 232
Replace Type Code with State/Strategy . . . 239
Replace Subclass with Fields . . . 251
Lazily Initialized Attribute . . . 255
Eagerly Initialized Attribute . . . 257
Chapter 9: Simplifying Conditional Expressions . . . 261
Decompose Conditional . . . 261
Recompose Conditional . . . 264
Consolidate Conditional Expression . . . 265
Consolidate Duplicate Conditional Fragments . . . 268
Remove Control Flag . . . 269
Replace Nested Conditional with Guard Clauses . . . 274
Replace Conditional with Polymorphism . . . 279
Introduce Null Object . . . 284
Introduce Assertion . . . 292
Chapter 10: Making Method Calls Simpler . . . 297
Rename Method . . . 298
Add Parameter . . . 300
Remove Parameter . . . 302
Separate Query from Modifier . . . 303
Parameterize Method . . . 307
Replace Parameter with Explicit Methods . . . 310
Preserve Whole Object . . . 313
Replace Parameter with Method . . . 317
Introduce Parameter Object . . . 320
Remove Setting Method . . . 324
Hide Method . . . 327
Replace Constructor with Factory Method . . . 328
Replace Error Code with Exception . . . 332
Replace Exception with Test . . . 337
Introduce Gateway . . . 341
Introduce Expression Builder . . . 346
Chapter 11: Dealing with Generalization . . . 353
Pull Up Method . . . 353
Push Down Method . . . 356
Extract Module . . . 357
Inline Module . . . 362
Extract Subclass . . . 363
Introduce Inheritance . . . 368
Collapse Heirarchy . . . 371
Form Template Method . . . 372
Replace Inheritance with Delegation . . . 386
Replace Delegation with Hierarchy . . . 389
Replace Abstract Superclass with Module . . . 392
Chapter 12: Big Refactorings . . . 397
The Nature of the Game . . . 397
Why Big Refactorings Are Important . . . 398
Four Big Refactorings . . . 398
Tease Apart Inheritance . . . 399
Convert Procedural Design to Objects . . . 405
Separate Domain from Presentation . . . 406
Extract Hierarchy . . . 412
Chapter 13: Putting It All Together . . . 417
References . . . 421
Index . . . 423
About the Author :
Jay Fields is a software developer for DRW Trading and a frequent conference presenter. Jay has a passion for discovering and maturing innovative solutions. Jay’s website is available at www.jayfields.com.
Shane Harvie has delivered software in Agile environments in the United States, India, and Australia. He works for DRW Trading in Chicago and blogs at www.shaneharvie.com.
Martin Fowler is Chief Scientist at ThoughtWorks and one of the world’s leading experts in the effective design of enterprise software. He has pioneered object-oriented development, patterns, agile methodologies, domain modeling, UML, and Extreme Programming. His books include Refactoring, Analysis Patterns, and UML Distilled. His book, Patterns of Enterprise Application Architecture, won Software Development’s Jolt Productivity Award and Javaworld.com’s best Java book award.
