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The Ruby Programming Language

Cover of The Ruby Programming Language by Yukihiro Matsumoto... Published by O'Reilly Media, Inc.
  1. The Ruby Programming Language
    1. SPECIAL OFFER: Upgrade this ebook with O’Reilly
    2. A Note Regarding Supplemental Files
    3. Preface
      1. Acknowledgments
      2. Conventions Used in This Book
      3. Using Code Examples
      4. How to Contact Us
      5. Safari® Enabled
    4. 1. Introduction
      1. A Tour of Ruby
      2. Try Ruby
      3. About This Book
      4. A Sudoku Solver in Ruby
    5. 2. The Structure and Execution of Ruby Programs
      1. Lexical Structure
      2. Syntactic Structure
      3. File Structure
      4. Program Encoding
      5. Program Execution
    6. 3. Datatypes and Objects
      1. Numbers
      2. Text
      3. Arrays
      4. Hashes
      5. Ranges
      6. Symbols
      7. True, False, and Nil
      8. Objects
    7. 4. Expressions and Operators
      1. Literals and Keyword Literals
      2. Variable References
      3. Constant References
      4. Method Invocations
      5. Assignments
      6. Operators
    8. 5. Statements and Control Structures
      1. Conditionals
      2. Loops
      3. Iterators and Enumerable Objects
      4. Blocks
      5. Altering Control Flow
      6. Exceptions and Exception Handling
      7. BEGIN and END
      8. Threads, Fibers, and Continuations
    9. 6. Methods, Procs, Lambdas, and Closures
      1. Defining Simple Methods
      2. Method Names
      3. Methods and Parentheses
      4. Method Arguments
      5. Procs and Lambdas
      6. Closures
      7. Method Objects
      8. Functional Programming
    10. 7. Classes and Modules
      1. Defining a Simple Class
      2. Method Visibility: Public, Protected, Private
      3. Subclassing and Inheritance
      4. Object Creation and Initialization
      5. Modules
      6. Loading and Requiring Modules
      7. Singleton Methods and the Eigenclass
      8. Method Lookup
      9. Constant Lookup
    11. 8. Reflection and Metaprogramming
      1. Types, Classes, and Modules
      2. Evaluating Strings and Blocks
      3. Variables and Constants
      4. Methods
      5. Hooks
      6. Tracing
      7. ObjectSpace and GC
      8. Custom Control Structures
      9. Missing Methods and Missing Constants
      10. Dynamically Creating Methods
      11. Alias Chaining
      12. Domain-Specific Languages
    12. 9. The Ruby Platform
      1. Strings
      2. Regular Expressions
      3. Numbers and Math
      4. Dates and Times
      5. Collections
      6. Files and Directories
      7. Input/Output
      8. Networking
      9. Threads and Concurrency
    13. 10. The Ruby Environment
      1. Invoking the Ruby Interpreter
      2. The Top-Level Environment
      3. Practical Extraction and Reporting Shortcuts
      4. Calling the OS
      5. Security
    14. Index
    15. About the Authors
    16. Colophon
    17. SPECIAL OFFER: Upgrade this ebook with O’Reilly

Alias Chaining

As we’ve seen, metaprogramming in Ruby often involves the dynamic definition of methods. Just as common is the dynamic modification of methods. Methods are modified with a technique we’ll call alias chaining.[6] It works like this:

  • First, create an alias for the method to be modified. This alias provides a name for the unmodified version of the method.

  • Next, define a new version of the method. This new version should call the unmodified version through the alias, but it can add whatever functionality is needed before and after it does that.

Note that these steps can be applied repeatedly (as long as a different alias is used each time), creating a chain of methods and aliases.

This section includes three alias chaining examples. The first performs the alias chaining statically; i.e., using regular alias and def statements. The second and third examples are more dynamic; they alias chain arbitrarily named methods using alias_method, define_method, and class_eval.

Tracing Files Loaded and Classes Defined

Example 8-8 is code that keeps track of all files loaded and all classes defined in a program. When the program exits, it prints a report. You can use this code to “instrument” an existing program so that you better understand what it is doing. One way to use this code is to insert this line at the beginning of the program:

require 'classtrace'

An easier solution, however, is to use the -r option to your Ruby interpreter:

ruby -rclasstrace my_program.rb --traceout /tmp/trace ...

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