Learning Perl Objects, References, and Modules

Transcription

1 Learning Perl Objects, References, and Modules Randal L. Schwartz with Tom Phoenix HLuHB Darmstadt Illlllllllllllllllllllll O'REILLY* Beijing Cambridge Farnham Koln Paris Sebastopol Taipei Tokyo

2 Foreword Preface ix xi 1. Introduction 1 What Should You Know Already? 2 What About All Those Footnotes? 2 What's with the Exercises? 2 What if I'm a Perl Course Instructor? 3 2. Building Larger Programs 4 The Cure for the Common Code 4 Inserting Code with eval 5 Using do 6 Using require 8 require 9 The Problem of Namespace Collisions 11 Packages as Namespace Separators 12 Scope of a Package Directive 14 Packages and Lexicals 15 Exercises Introduction to References...; 17 Performing the Same Task on Many Arrays 17 Taking a Reference to an Array 19 Dereferencing the Array Reference 20 Dropping Those Braces 21 Modifying the Array 22

3 Nested Data Structures 23 Simplifying Nested Element References with Arrows 25 References to Hashes 26 Exercises References and Scoping 30 More than One Reference to Data 30 What if That Was the Name? 31 Reference Counting and Nested Data Structures 32 When Reference Counting Goes Bad 34 Creating an Anonymous Array Directly 35 Creating an Anonymous Hash 38 Autovivification 40 Autovivification and Hashes 42 Exercises Manipulating Complex Data Structures 45 Using the Debugger to View Complex Data 45 Viewing Complex Data with Data::Dumper 50 Storing Complex Data with Storable 51 The map and grep Operators 53 Using map.55 Applying a Bit of Indirection 56 Selecting and Altering Complex Data 58 Exercises Subroutine References 61 Referencing a Named Subroutine 61 Anonymous Subroutines 65 Callbacks 67 Closures 68 Returning a Subroutine from a Subroutine 70 Closure Variables as Inputs 73 Closure Variables as Static Local Variables 73 Exercise Practical Reference Tricks 77 Review of Sorting 77 Sorting with Indices 78

4 I Sorting Efficiently 79 The Schwartzian Transform 81 Recursively Defined Data 82 Building Recursively Defined Data 82 Displaying Recursively Defined Data 85 Exercises Introduction to Objects 88 If We Could Talk to the Animals Introducing the Method Invocation Arrow 90 The Extra Parameter of Method Invocation 91 Calling a Second Method to Simplify Things 92 A Few Notes 93 Overriding the Methods 94 Starting the Search from a Different Place 96 The SUPER Way of Doing Things 97 What to Do 97 Where We Are So Far Exercises Objects with Data 99 A Horse Is a Horse, of Course of Course or Is It? 99 Invoking an Instance Method 100 Accessing the Instance Data 101 How to Build a Horse 102 Inheriting the Constructor 102 Making a Method Work with Either Classes or Instances 103 Adding Parameters to a Method 104 More Interesting Instances 105 A Horse of a Different Color 106 Getting Your Deposit Back 106 Don't Look Inside the Box 108 Faster Getters and Setters 109 Getters That Double as Setters 109 Restricting a Method to Class-Only or Instance-Only 110 Exercise 110

5 10. Object Destruction 112 Beating a Dead Horse 117 Indirect Object Notation 118 Additional Instance Variables in Subclasses 119 Using Class Variables 121 Weakening the Argument 122 Exercise Some Advanced Object Topics 126 UNIVERSAL Methods 126 Testing Your Objects for Good Behavior 127 AUTOLOAD as a Last Resort 128 Using AUTOLOAD for Accessors 129 Creating Getters and Setters More Easily 130 Multiple Inheritance 132 References to Filehandles 133 Exercise Using Modules 137 Sample Function-Oriented Interface: File::Basename 137 Selecting What to Import 138 Sample Object-Oriented Interface: File::Spec 138 A More Typical Object-Oriented Module: Math::BigInt 139 The Differences Between OO and Non-OO Modules 140 What use Is Doing 140 Setting the Path at the Right Time 141 Importing with Exporter 143 EXPORT 144 Exporting in a Primarily OO Module 145 Custom Import Routines 147 Exercise Writing a Distribution 148 Starting with h2xs 149 Looking at the Templates 149 The Prototype Module Itself 152 Embedded Documentation 154 Controlling the Distribution withmakefile.pl 158 Alternate Installation Locations (PREFIX=...) 159

6 Trivial make test 160 Trivial make install 161 Trivial make dist 162 Using the Alternate Library Location 162 Exercise Essential Testing 164 What the Test Harness Does 166 Writing Tests with Test: :Simple 167 Writing Tests with Test::More 168 Conditional Tests 172 More Complex Tests (Multiple Test Scripts) 173 Testing Things That Write to STDOUT and STDERR 173 Exercise Contributing to CPAN 175 The Comprehensive Perl Archive Network 175 Getting Prepared 176 Preparing Your Distribution 176 Uploading Your Distribution 177 Announcing the Module 178 Testing on Multiple Platforms 178 Consider Writing an Article or Giving a Talk 178 Exercise 179 Appendix. Answers to Exercises 181 Index 197