Eloquent Ruby

Russ Olsen  
Total pages
February 2011
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Eloquent Ruby
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Table of Contents

Foreword xix

Preface xxi

Acknowledgments xxv

About the Author xxvii

PART I: The Basics 1

Chapter 1: Write Code That Looks Like Ruby 3

The Very Basic Basics 4

Go Easy on the Comments 6

Camels for Classes, Snakes Everywhere Else 8

Parentheses Are Optional but Are Occasionally Forbidden 9

Folding Up Those Lines 10

Folding Up Those Code Blocks 11

Staying Out of Trouble 12

In the Wild 13

Wrapping Up 15

Chapter 2: Choose the Right Control Structure 17

If, Unless, While, and Until 17

Use the Modifier Forms Where Appropriate 19

Use each, Not for 20

A Case of Programming Logic 21

Staying Out of Trouble 23

In the Wild 25

Wrapping Up 27

Chapter 3: Take Advantage of Ruby’s Smart Collections 29

Literal Shortcuts 29

Instant Arrays and Hashes from Method Calls 30

Running Through Your Collection 33

Beware the Bang! 36

Rely on the Order of Your Hashes 38

In the Wild 38

Staying Out of Trouble 40

Wrapping Up 42

Chapter 4: Take Advantage of Ruby’s Smart Strings 43

Coming Up with a String 44

Another API to Master 47

The String: A Place for Your Lines, Characters, and Bytes 49

In the Wild 50

Staying Out of Trouble 51

Wrapping Up 52

Chapter 5: Find the Right String with Regular Expressions 53

Matching One Character at a Time 54

Sets, Ranges, and Alternatives 55

The Regular Expression Star 57

Regular Expressions in Ruby 58

Beginnings and Endings 60

In the Wild 62

Staying Out of Trouble 63

Wrapping Up 64

Chapter 6: Use Symbols to Stand for Something 65

The Two Faces of Strings 65

Not Quite a String 66

Optimized to Stand for Something 67

In the Wild 69

Staying Out of Trouble 70

Wrapping Up 71

Chapter 7: Treat Everything Like an Object–Because Everything Is 73

A Quick Review of Classes, Instances, and Methods 74

Objects All the Way Down 76

The Importance of Being an Object 77

Public, Private, and Protected 79

In the Wild 81

Staying Out of Trouble 82

Wrapping Up 84

Chapter 8: Embrace Dynamic Typing 85

Shorter Programs, But Not the Way You Think 85

Extreme Decoupling 89

Required Ceremony Versus Programmer-Driven Clarity 92

Staying Out of Trouble 93

In the Wild 94

Wrapping Up 96

Chapter 9: Write Specs! 97

Test::Unit: When Your Documents Just Have to Work 98

A Plethora of Assertions 101

Don’t Test It, Spec It! 101

A Tidy Spec Is a Readable Spec 104

Easy Stubs 105

. . . And Easy Mocks 107

In the Wild 108

Staying Out of Trouble 110

Wrapping Up 113

PART II: Classes, Modules, and Blocks 115

Chapter 10: Construct Your Classes from Short, Focused Methods 117

Compressing Specifications 117

Composing Methods for Humans 121

Composing Ruby Methods 122

One Way Out? 123

Staying Out of Trouble 126

In the Wild 127

Wrapping Up 128

Chapter 11: Define Operators Respectfully 129

Defining Operators in Ruby 129

A Sampling of Operators 131

Operating Across Classes 134

Staying Out of Trouble 135

In the Wild 137

Wrapping Up 139

Chapter 12: Create Classes That Understand Equality 141

An Identifier for Your Documents 141

An Embarrassment of Equality 142

Double Equals for Everyday Use 143

Broadening the Appeal of the == Method 145

Well-Behaved Equality 146

Triple Equals for Case Statements 149

Hash Tables and the eql? Method 150

Building a Well-Behaved Hash Key 152

Staying Out of Trouble 153

In the Wild 154

Wrapping Up 156

Chapter 13: Get the Behavior You Need with Singleton and Class Methods 157

A Stubby Puzzle 158

A Hidden, but Real Class 160

Class Methods: Singletons in Plain Sight 162

In the Wild 164

Staying Out of Trouble 165

Wrapping Up 167

Chapter 14: Use Class Instance Variables 169

A Quick Review of Class Variables 169

Wandering Variables 171

Getting Control of the Data in Your Class 174

Class Instance Variables and Subclasses 175

Adding Some Convenience to Your Class Instance Variables 176

In the Wild 177

Staying Out of Trouble 179

Wrapping Up 179

Chapter 15: Use Modules as Name Spaces 181

A Place for Your Stuff, with a Name 181

A Home for Those Utility Methods 184

Building Modules a Little at a Time 185

Treat Modules Like the Objects That They Are 186

Staying Out of Trouble 189

In the Wild 190

Wrapping Up 191

Chapter 16: Use Modules as Mixins 193

Better Books with Modules 193

Mixin Modules to the Rescue 195

Extending a Module 197

Staying Out of Trouble 198

In the Wild 202

Wrapping Up 205

Chapter 17: Use Blocks to Iterate 207

A Quick Review of Code Blocks 207

One Word after Another 209

As Many Iterators as You Like 210

Iterating over the Ethereal 211

Enumerable: Your Iterator on Steroids 213

Staying Out of Trouble 215

In the Wild 217

Wrapping Up 218

Chapter 18: Execute Around with a Block 219

Add a Little Logging 219

When It Absolutely Must Happen 224

Setting Up Objects with an Initialization Block 225

Dragging Your Scope along with the Block 225

Carrying the Answers Back 227

Staying Out of Trouble 228

In the Wild 229

Wrapping Up 231

Chapter 19: Save Blocks to Execute Later 233

Explicit Blocks 233

The Call Back Problem 234

Banking Blocks 236

Saving Code Blocks for Lazy Initialization 237

Instant Block Objects 239

Staying Out of Trouble 240

In the Wild 243

Wrapping Up 244

PART III: Metaprogramming 247

Chapter 20: Use Hooks to Keep Your Program Informed 249

Waking Up to a New Subclass 250

Modules Want To Be Heard Too 253

Knowing When Your Time Is Up 255

. . . And a Cast of Thousands 256

Staying Out of Trouble 257

In the Wild 259

Wrapping Up 261

Chapter 21: Use method_missing for Flexible Error Handling 263

Meeting Those Missing Methods 264

Handling Document Errors 266

Coping with Constants 267

In the Wild 268

Staying Out of Trouble 270

Wrapping Up 271

Chapter 22: Use method_missing for Delegation 273

The Promise and Pain of Delegation 274

The Trouble with Old-Fashioned Delegation 275

The method_missing Method to the Rescue 277

More Discriminating Delegation 278

Staying Out of Trouble 279

In the Wild 281

Wrapping Up 283

Chapter 23: Use method_missing to Build Flexible APIs 285

Building Form Letters One Word at a Time 286

Magic Methods from method_missing 287

It’s the Users That Count–All of Them 289

Staying Out of Trouble 289

In the Wild 290

Wrapping Up 292

Chapter 24: Update Existing Classes with Monkey Patching 293

Wide-Open Classes 294

Fixing a Broken Class 295

Improving Existing Classes 296

Renaming Methods with alias_method 297

Do Anything to Any Class, Anytime 299

In the Wild 299

Staying Out of Trouble 303

Wrapping Up 303

Chapter 25: Create Self-Modifying Classes 305

Open Classes, Again 305

Put Programming Logic in Your Classes 308

Class Methods That Change Their Class 309

In the Wild 310

Staying Out of Trouble 314

Wrapping Up 315

Chapter 26: Create Classes That Modify Their Subclasses 317

A Document of Paragraphs 317

Subclassing Is (Sometimes) Hard to Do 319

Class Methods That Build Instance Methods 321

Better Method Creation with define_method 324

The Modification Sky Is the Limit 324

In the Wild 327

Staying Out of Trouble 330

Wrapping Up 332

PART IV: Pulling It All Together 333

Chapter 27: Invent Internal DSLs 335

Little Languages for Big Problems 335

Dealing with XML 336

Stepping Over the DSL Line 341

Pulling Out All the Stops 344

In the Wild 345

Staying Out of Trouble 347

Wrapping Up 349

Chapter 28: Build External DSLs for Flexible Syntax 351

The Trouble with the Ripper 352

Internal Is Not the Only DSL 353

Regular Expressions for Heavier Parsing 356

Treetop for Really Big Jobs 358

Staying Out of Trouble 360

In the Wild 362

Wrapping Up 364

Chapter 29: Package Your Programs as Gems 367

Consuming Gems 367

Gem Versions 368

The Nuts and Bolts of Gems 369

Building a Gem 370

Uploading Your Gem to a Repository 374

Automating Gem Creation 375

In the Wild 376

Staying Out of Trouble 377

Wrapping Up 380

Chapter 30: Know Your Ruby Implementation 381

A Fistful of Rubies 381

MRI: An Enlightening Experience for the C Programmer 382

YARV: MRI with a Byte Code Turbocharger 385

JRuby: Bending the “J” in the JVM 387

Rubinius 388

In the Wild 389

Staying Out of Trouble 389

Wrapping Up 390

Chapter 31: Keep an Open Mind to Go with Those Open Classes 391

Appendix: Going Further 393

Index 397


Russ Olsen’s career spans three decades, during which he has written everything from graphics device drivers to document management applications. These days, he diligently codes GIS, web service security, and process automation solutions. He spends much of his otherwise free time writing and speaking about programming, especially Ruby and Clojure. His first book was the highly regarded Design Patterns In Ruby (Addison-Wesley, 2007). He is also the lurking presence behind the Technology As If People Mattered blog at www.russolsen.com.

Reader Review(s)

"R>Eloquent Ruby is like programming in Ruby itself: fun, surprisingly deep, and you'll find yourself wishing it was always done this way. Wherever you are in your Ruby experience from novice to Rails developer, this book is a must read."

--Ethan Roberts

Owner, Monkey Mind LLC


"Eloquent Ruby lives up to its name. It's a smooth introduction to Ruby that's both well organized and enjoyable to read, as it covers all the essential topics in the right order. This is the book I wish I'd learned Ruby from."

--James Kebinger

Senior Software Engineer, PatientsLikeMe



"Ruby's syntactic and logical aesthetics represent the pinnacle for elegance and beauty in the ALGOL family of programming languages. Eloquent Ruby is the perfect book to highlight this masterful language and Russ's blend of wit and wisdom is certain to entertain and inform."

--Michael Fogus

Contributor to the Clojure programming language and author of The Joy of Clojure