Refactoring: Ruby Edition

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