Ruby Summary

  1. Ruby Modules are similar to classes in that they hold a collection of methods, constants, and other module and class definitions. Unlike classes, you cannot create objects based on modules; instead, you specify that you want the functionality of a particular module to be added to the functionality of a class, or of a specific object.
  2. Modules serve two purposes: First they act as namespace, letting you define methods whose names will not clash with those defined elsewhere. Second, they allow you to share functionality between classes - if a class mixes in a module, that module's instance methods become available as if they had been defined in the class. They get mixed in.
  3. Observe how we use require or load. require and load take strings as their arguments.

    require 'motorcycle' or load 'motorcycle.rb'

    include takes the name of a module, in the form of a constant, as in include 'Stuff'.

    The include method accepts any number of Module objects to mix in:
    include Enumerable, Comparable

    Although every class is a module, the include method does not allow a class to be included within another class.
  4. Remember that you can mix in more than one module in a class. However, a class cannot inherit from more than one class.
  5. Class names tend to be nouns, while module names are often adjectives.
  6. At every point when your program is running, there is one and only one self - the current or default object accessible to you in your program.
  7. Please note the rules given for self in the Self related page.
  8. Java features the ability to serialize objects, letting you store them somewhere and reconstitute them when needed. Ruby calls this kind of serialization marshaling.
  9. Marshal.dump is used to save a serialized version of an object.
  10. Marshal.load is used to read in from a serialized object.
  11. A Ruby constant is a reference to an object.
  12. Although constants should not be changed, you can modify the internal states of the objects they reference.
  13. Remember the rules for constants.

Note: The Ruby Logo is Copyright (c) 2006, Yukihiro Matsumoto. I have made extensive references to information, related to Ruby, available in the public domain (wikis and the blogs, articles of various Ruby Gurus), my acknowledgment and thanks to all of them. Much of the material on and in the course at is drawn primarily from the Programming Ruby book, available from The Pragmatic Bookshelf.