Metaprogramming Ruby 2: Program Like the Ruby Pros

262 Pages·2014·14.41 MB·English

by  Paolo Perrotta

What Readers Are Saying About
Metaprogramming Ruby 2
This is the one book about Ruby that makes you go “So that’s how it works” over
and over again, as concepts such as the object model, DSLs, and blocks fall into
place with that satisfying “Click!” sound. It’s a great guide to what happens under
the hood of a language that seems to involve a kind of magic deep inside. I highly
recommend it.
➤ Peter Bakhirev
Lead software engineer, Gilt City
The previous edition of Metaprogramming Ruby changed my life and my code, and
helped me get my first programming job. You would think there would be no way
to improve on a book that good, but Paolo Perrotta has done it. Learn to unlock
the hidden potential of this beautiful language, and fall in love with Ruby again.
➤ Richard Schneeman
Programmer, Heroku
For gem authors and application developers alike, this book lays down the foun-
dation everyone needs to harness the full power of Ruby. Paolo describes
metaprogramming in a fun and approachable way for all skill levels. The knowledge
garnered from reading this book will help you write cleaner code and work more
effectively with legacy codebases.
➤ Paul Elliott
Rocketeer, Hashrocket
If you want to follow the path of Ruby metaprogramming mastery, then this book
is the best companion you can think of, no matter what your level is. I had
struggled with Ruby metaprogramming for years until I read this book; now it all
makes sense.
➤ Fabien Catteau
Software developer, Tech-Angels
This is a book that everyone who wants to have a deeper understanding of the
inner workings of Ruby and Ruby on Rails should read. The “spells” described in
this book are invaluable tools to understand and use Ruby to its full extent. This
is not only about metaprogramming, but also about taking your Ruby programming
to a different level.
➤ Kosmas Chatzimichalis
Software engineer
I’m a huge Python fan, so I was supposed to disregard Ruby. Paolo made me ap-
preciate it. Not only is Metaprogramming Ruby the book that allowed me to wrap
my head around this esoteric and fascinating topic, but it also made me rethink
the way I write code in other languages.
➤ Arialdo Martini
Programmer, JobRapido.com
This book uncovers all the ins and outs of the art of metaprogramming in Ruby,
with a no-nonsense approach and an irony that transpires from vibrant prose,
never boring, without compromising any of its insightfulness. Metaprogramming
Ruby is one of those books that any serious Rubyist (and even the pros) will want
to revisit from time to time.
➤ Piergiuliano Bossi
Principal engineer lead, Points
Metaprogramming Ruby has been a hugely influential book for me, especially
during a time when I wanted to learn about the inner workings of Ruby. Paolo
“Nusco” Perrotta made what is normally a complex topic fun, enjoyable, and very
approachable.
➤ Josh Kalderimis
CEO, Travis CI
Metaprogramming Ruby 2
Program Like the Ruby Pros
Paolo Perrotta
The Pragmatic Bookshelf
Dallas, Texas • Raleigh, North Carolina
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ISBN-13: 978-1-94122-212-6
Encoded using the finest acid-free high-entropy binary digits.
Book version: P1.0—August 2014
I was thirteen, and I was tired of hanging
out at the local toy shop to play Intellivision
games. I wanted my own videogame console.
I’d been bugging my parents for a while,
with no success.
Then I found an alternative: I could play
games on a computer as well. So I asked my
parents to buy me one of those new 8-bit
computers—you know, to learn useful stuff.
My dad agreed, and my mom took me to the
shop and bought me a Sinclair ZX Spectrum.
Mom, Dad… Here is something that I should’ve
told you more often in my life: thank you. This
book is dedicated to the two of you. I’m hoping
it will make you proud, just like your once-kid
is proud of you. And while I’m here, I have
something to confess about that life-changing
day thirty years ago: I didn’t really want to
learn stuff. I just wanted to play.
In fact, that’s what I’ve been doing
all these years.
Contents
Foreword . . . . . . . . . . . . . xiii
Acknowledgments . . . . . . . . . . . xv
Introduction . . . . . . . . . . . . xvii
Part I — Metaprogramming Ruby
1. The M Word . . . . . . . . . . . . . 3
Ghost Towns and Marketplaces 3
The Story of Bob, Metaprogrammer 4
Metaprogramming and Ruby 7
2. Monday: The Object Model . . . . . . . . . 11
Open Classes 11
Inside the Object Model 16
Quiz: Missing Lines 26
What Happens When You Call a Method? 27
Quiz: Tangle of Modules 39
Wrap-Up 42
3. Tuesday: Methods . . . . . . . . . . . 45
A Duplication Problem 46
Dynamic Methods 48
method_missing 55
Quiz: Bug Hunt 64
Blank Slates 66
Wrap-Up 69
4. Wednesday: Blocks . . . . . . . . . . . 73
The Day of the Blocks 73
Quiz: Ruby# 75
Contents • x
Blocks Are Closures 77
instance_eval() 85
Callable Objects 88
Writing a Domain-Specific Language 96
Quiz: A Better DSL 98
Wrap-Up 103
5. Thursday: Class Definitions . . . . . . . . 105
Class Definitions Demystified 106
Quiz: Class Taboo 112
Singleton Methods 113
Singleton Classes 118
Quiz: Module Trouble 129
Method Wrappers 131
Quiz: Broken Math 136
Wrap-Up 137
6. Friday: Code That Writes Code . . . . . . . . 139
Coding Your Way to the Weekend 139
Kernel#eval 141
Quiz: Checked Attributes (Step 1) 150
Quiz: Checked Attributes (Step 2) 153
Quiz: Checked Attributes (Step 3) 154
Quiz: Checked Attributes (Step 4) 156
Hook Methods 157
Quiz: Checked Attributes (Step 5) 160
Wrap-Up 162
7. Epilogue . . . . . . . . . . . . . 163
Part II — Metaprogramming in Rails
8. Preparing for a Rails Tour . . . . . . . . . 167
Ruby on Rails 168
Installing Rails 168
The Rails Source Code 168
9. The Design of Active Record . . . . . . . . 171
A Short Active Record Example 171
How Active Record Is Put Together 172
A Lesson Learned 176