Ruby is famous for being easy to learn, but most users only scratch the surface of what it can do. While other books focus on Ruby’s trendy features, The Book of ™ Ruby reveals the secret inner workings of one of the world’s most popular programming languages, teaching you to write clear, maintainable code. You’ll start with the basics—types, data structures, and control flows—and progress to advanced features like blocks, mixins, metaclasses, and beyond. Rather than bog you down with a lot of theory, The Book of Ruby takes a hands-on approach and focuses on making you productive from day one. As you follow along, you’ll learn to: • Leverage Ruby’s succinct and flexible syntax to maximize your productivity • Balance Ruby’s functional, imperative, and object- oriented features • Write self-modifying programs using dynamic programming techniques • Create new fibers and threads for lightweight multitasking MASTER RUBY FROM THE INSIDE OUT MASTER RUBY FROM THE INSIDE OUT • Catch and recover from execution errors with robust exception handling • Develop powerful web applications with the Ruby on Rails framework Each chapter includes a “Digging Deeper” section that shows you how Ruby works under the hood, so you won’t be caught off guard by its deceptively simple scoping, multithreading features, or precedence rules. Whether you’re new to programming or just new to Ruby, The Book of Ruby is your guide to mastering rapid, real-world software development with this unique and elegant language. ABOUT THE AUTHOR Huw Collingbourne is the Director of Technology for SapphireSteel Software, developer of the Ruby In Steel IDE. With 30 years of programming experience, he has written programming columns for numerous magazines, presented features on computing for BBC Television, and currently edits the online technical journal Bitwise Magazine. He has previously released two free ebooks on Ruby—The Little Book of Ruby and The Book of Ruby. Covers Ruby 1.8 and 1.9 SHELVE IN : COMPUTERS/PROGRAMMING LANGUAGES/RUBY $39.95 ($45.95 CDN) www.nostarch.com THE FINEST IN GEEK ENTERTAINMENT ™ “I LIE FLAT.” This book uses a lay-flat binding that won’t snap shut. FSC LOGO HUW COLLINGBOURNE THE BOOK OF RUBY THE BOOK OF RUBY A HANDS-ON GUIDE FOR THE ADVENTUROUS ™ ™ THE BOOK OF RUBY THE BOOK OF RUBY COLLINGBOURNE www.it-ebooks.info www.it-ebooks.info THE BOOK OF ™ RUBY www.it-ebooks.info www.it-ebooks.info THE BOOK OF ™ RUBY A Hands-On Guide for the Adventurous by Huw Collingbourne San Francisco www.it-ebooks.info THE BOOK OF RUBY. Copyright © 2011 by Huw Collingbourne All rights reserved. No part of this work may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval system, without the prior written permission of the copyright owner and the publisher. Printed in Canada 15 14 13 12 11 1 2 3 4 5 6 7 8 9 ISBN-10: 1-59327-294-4 ISBN-13: 978-1-59327-294-4 Publisher: William Pollock Production Editor: Serena Yang Developmental Editor: Keith Fancher Technical Reviewer: Pat Eyler Copyeditor: Kim Wimpsett Compositors: Serena Yang and Alison Law Proofreader: Ward Webber For information on book distributors or translations, please contact No Starch Press, Inc. directly: No Starch Press, Inc. 38 Ringold Street, San Francisco, CA 94103 phone: 415.863.9900; fax: 415.863.9950; info@nostarch.com; www.nostarch.com Library of Congress Cataloging-in-Publication Data Collingbourne, Huw. The book of Ruby : a hands-on guide for the adventurous / Huw Collingbourne. p. cm. Includes index. ISBN-13: 978-1-59327-294-4 ISBN-10: 1-59327-294-4 1. Ruby (Computer program language) 2. Object-oriented programming (Computer science) I. Title. QA76.73.R83C65 2011 005.1'17 dc23 2011014782 No Starch Press and the No Starch Press logo are registered trademarks of No Starch Press, Inc. “The Book of” is a trademark of No Starch Press, Inc. Other product and company names mentioned herein may be the trademarks of their respective owners. Rather than use a trademark symbol with every occurrence of a trademarked name, we are using the names only in an editorial fashion and to the benefit of the trademark owner, with no intention of infringement of the trademark. The information in this book is distributed on an “As Is” basis, without warranty. While every precaution has been taken in the preparation of this work, neither the author nor No Starch Press, Inc. shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indirectly by the information contained in it. www.it-ebooks.info BRIEF CONTENTS Acknowledgments xv Introduction xvii Chapter 1: Strings, Numbers, Classes, and Objects 1 Chapter 2: Class Hierarchies, Attributes, and Class Variables 15 Chapter 3: Strings and Ranges 33 Chapter 4: Arrays and Hashes 47 Chapter 5: Loops and Iterators 67 Chapter 6: Conditional Statements 83 Chapter 7: Methods 97 Chapter 8: Passing Arguments and Returning Values 121 Chapter 9: Exception Handling 139 Chapter 10: Blocks, Procs, and Lambdas 155 Chapter 11: Symbols 181 Chapter 12: Modules and Mixins 191 Chapter 13: Files and IO 213 Chapter 14: YAML 227 Chapter 15: Marshal 239 www.it-ebooks.info vi Brief Contents Chapter 16: Regular Expressions 249 Chapter 17: Threads 263 Chapter 18: Debugging and Testing 283 Chapter 19: Ruby on Rails 299 Chapter 20: Dynamic Programming 325 Appendix A: Documenting Ruby with RDoc 345 Appendix B: Installing MySQL for Ruby on Rails 349 Appendix C: Further Reading 353 Appendix D: Ruby and Rails Development Software 357 Index 361 www.it-ebooks.info CONTENTS IN DETAIL ACKNOWLEDGMENTS xv INTRODUCTION xvii What Is Ruby? xviii What Is Rails? xviii Matters of Ruby Style xviii How to Read This Book xix Digging Deeper xix Making Sense of the Text xix Downloading Ruby xx Getting the Source Code of the Sample Programs xxi Running Ruby Programs xxi The Ruby Library Documentation xxi 1 STRINGS, NUMBERS, CLASSES, AND OBJECTS 1 Getting and Putting Input 2 Strings and Embedded Evaluation 2 Numbers 3 Comments 4 Testing a Condition: if then 4 Local and Global Variables 5 Classes and Objects 6 Instance Variables 7 Retrieving Data from an Object 7 Messages, Methods, and Polymorphism 9 Constructors: new and initialize 10 Inspecting Objects 11 2 CLASS HIERARCHIES, ATTRIBUTES, AND CLASS VARIABLES 15 Superclasses and Subclasses 17 Passing Arguments to the Superclass 18 Accessor Methods 19 Attribute Readers and Writers 20 Calling Methods of a Superclass 23 Class Variables 23 Digging Deeper 25 Superclasses 25 The Root of All Classes 29 Constants Inside Classes 30 Partial Classes 30 www.it-ebooks.info viii Contents in Detail 3 STRINGS AND RANGES 33 User-Defined String Delimiters 35 Backquotes 36 String Handling 36 Concatenation 37 What About Commas? 38 String Assignment 38 Indexing into a String 39 Removing Newline Characters: chop and chomp 42 Format Strings 43 Ranges 43 Ranges of Strings 44 Iterating with a Range 44 Digging Deeper 45 Heredocs 45 String Literals 46 4 ARRAYS AND HASHES 47 Arrays 47 Creating Arrays 48 Multidimensional Arrays 50 Iterating over Arrays 51 Indexing into Arrays 52 Copying Arrays 53 Testing Arrays for Equality 53 Sorting Arrays 54 Comparing Values 55 Array Methods 57 Hashes 58 Creating Hashes 58 Indexing into a Hash 60 Copying a Hash 60 Hash Order 60 Sorting a Hash 61 Hash Methods 62 Digging Deeper 63 Treating Hashes as Arrays 63 Appending vs. Concatenating 63 Vectors and Matrices 64 Sets 65 5 LOOPS AND ITERATORS 67 for Loops 67 Blocks and Block Parameters 70 Iterating upto and downto 70 www.it-ebooks.info [...]... example, this is the command you would enter in order to run the helloworld.rb program: ruby helloworld.rb If you use a Ruby IDE, you may be able to load the Ruby programs into the IDE and run them using the integrated tools of that IDE The Ruby Library Documentation The Book of Ruby covers many of the classes and methods in the standard Ruby library—but by no means all of them! At some stage, therefore,... hazards along the way www.it-ebooks.info The Book of Ruby describes versions 1.8.x and 1.9.x of the Ruby language In most respects, Ruby 1.8 and 1.9 are very similar, and most programs written for one version will run unmodified in the other There are important exceptions to this rule, however, and these are noted in the text Ruby 1.9 may be regarded as a stepping stone toward Ruby 2.0 At the time of writing,... persuade you of the merits of the Ruby language Instead, I’ll take the somewhat unconventional step of starting with a warning: Many people are attracted to Ruby by its simple syntax and its ease of use They are wrong Ruby s syntax may look simple at first sight, but the more you get to know the language, the more you will realize that it is, on the contrary, extremely complex The plain fact of the matter... installing Ruby using the Ruby Installer, available at http://www.rubyinstaller.org/ There are also several alternative implementations of Ruby, the most established of which is JRuby You can find information on where to download these implementations in Appendix D xx I n t r od u ct i on www.it-ebooks.info Getting the Source Code of the Sample Programs All the programs in every chapter in this book are... that Ruby has a number of pitfalls just waiting for unwary programmers to drop into In this book, it is my aim to guide you safely over the pitfalls and lead you through the choppy waters of Ruby s syntax and class libraries In the process, I’ll be exploring both the smooth, well-paved highways and the gnarlier, bumpy little byways of Ruby By the end of the journey, you should be able to use Ruby safely... representation of a Treasure object The method name, to_s, is not arbitrary the same method name is used throughout the standard Ruby object hierarchy In fact, the to_s method is defined for the Object class itself, which is the ultimate ancestor of all other classes in Ruby (with the exception of the BasicObject class, which you’ll look at more closely in the next chapter) By redefining the to_s method,... aspects of Ruby (including a few of those gnarly byways I mentioned a moment ago) in greater depth In many cases, you could skip the “Digging Deeper” sections and still learn all the Ruby you will ever need On the other hand, it is in these sections that you will often get closest to the inner workings of Ruby, so if you skip them, you are going to miss out on some pretty interesting stuff Making Sense of. .. instance variables, and you can set the values of all of them with the single initialize method rather than with many separate “set” methods; second, if the variables are all automatically initialized at the time of object creation, you will never end up with an “empty” variable (like the “nil” value returned when you tried to display the name of someotherdog in the previous program) Finally, I have... stuff Making Sense of the Text In The Book of Ruby, Ruby source code is written like this: def saysomething puts( "Hello" ) end Often the code will be annotated with comments Ruby comments are any text following a hash mark (#) on a single line The comments are ignored by the Ruby interpreter When I want to draw attention to some I n t r o d u ct i on www.it-ebooks.info xix output that Ruby displays or... http://www.nostarch.com/boruby.htm When you unzip the programs, you will find that they are grouped into a set of directories—one for each chapter Running Ruby Programs It is often useful to keep a command window open in the source directory containing your Ruby program files Assuming that the Ruby interpreter is correctly pathed on your system, you will then be able to run programs by entering ruby programname . OF RUBY THE BOOK OF RUBY A HANDS-ON GUIDE FOR THE ADVENTUROUS ™ ™ THE BOOK OF RUBY THE BOOK OF RUBY COLLINGBOURNE www.it-ebooks.info www.it-ebooks.info THE BOOK OF ™ RUBY www.it-ebooks.info www.it-ebooks.info THE. and currently edits the online technical journal Bitwise Magazine. He has previously released two free ebooks on Ruby The Little Book of Ruby and The Book of Ruby. Covers Ruby 1.8 and 1.9 SHELVE. Ruby is famous for being easy to learn, but most users only scratch the surface of what it can do. While other books focus on Ruby s trendy features, The Book of ™ Ruby reveals the secret