Progr amming Ruby 1.9
The Pragmatic Programmers’ Guide
Dave Thomas
with Chad Fowler
and Andy Hunt
The Pragmatic Bookshelf
Raleigh, North Carolina Dallas, Texas
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Copyright
©
2
009 The Pra gmatic Programmers, LLC. All rights reserved. No part of this publication may be repro-
duced, stored in a retrieval system, or transmitted, in any form, or by any means, electronic, mechanical, photocopy-
ing, recording, or otherwise, without the prior consent of the publisher.
Printed in the United States of A merica.
ISBN: 1-934356-08-5
ISBN-13: 978-1-934356-08-1
Printing: P2.00, April 2009
Version: 2009-4-18
Text printed on acid-free paper.
Contents
FOREWORD 16
PREFACE 17
ROAD MAP 22
PA
RT I—FACETS OF RUBY
1 GETTING STAR TED 25
The Command P rompt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Installing Ruby . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Running Ruby . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Ruby Documentation: RDoc and ri . . . . . . . . . . . . . . . . . . . . . . . . 32
2 RU
BY.NEW 35
Ruby Is an Object-Oriented Language . . . . . . . . . . . . . . . . . . . . . . 35
Some Basic Ruby . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Arrays and Hashes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Control Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Regular Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Blocks and Iterators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Reading and ’Riting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Command-Line Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Onward and Upward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3 CL
ASSES, OBJECTS, AND VARIABLES 50
Objects and Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Classes Working with Other Classes . . . . . . . . . . . . . . . . . . . . . . . 58
Access Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Report erratum
4
CONTENTS 5
4 CONTAINERS, BLOCKS, AND ITERATORS 67
Blocks and Iterators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Containers Everywhere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
5 SH
ARING FUNCTIONALITY: INHERITANCE, MODULES, AND MIXINS 91
Inheritance and Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Mixins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Iterators and the Enumerable Module . . . . . . . . . . . . . . . . . . . . . . . 100
Composing Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Inheritance, Mixins, and Design . . . . . . . . . . . . . . . . . . . . . . . . . 104
6 STANDARD TYPES 106
Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
7 RE
GULAR EXPRESSIONS 117
What Regular Expressions Let You Do . . . . . . . . . . . . . . . . . . . . . . 117
Ruby’s Regular Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Digging Deeper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Pattern-Based Substitution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Advanced Regular Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . 130
8 MORE ABOUT METHODS 137
Defining a Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Calling a Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
9 EX
PRESSIONS 146
Operator Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Miscellaneous Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Conditional Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Case Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
Variable Scope, Loops, and Blocks . . . . . . . . . . . . . . . . . . . . . . . . 165
10 EX
CEPTIONS, CATCH, AND THROW 167
The Exception Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
Handling Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
Raising Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
Catch and Throw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
11 BASIC INPUT AND OUTPUT 176
What Is an IO Object? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
Opening and Closing Fil es . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Reading and Writing Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
Talking to Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
Report erratum
