Object/Class in Ruby about dylanninin.com

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Classes

 //ruby/class.c
 * class Classes and their hierarchy.
 * Terminology
 * - class: same as in Ruby.
 * - singleton class: class for a particular object
 * - eigenclass: = singleton class
 * - metaclass: class of a class. metaclass is a kind of singleton class.
 * - metametaclass: class of a metaclass.
 * - meta^(n)-class: class of a meta^(n-1)-class.
 * - attached object: A singleton class knows its unique instance.
 *   The instance is called the attached object for the singleton class.

Inheritances and Mixins

• inherit: superclass
  • Allows us to create new classes whose behavior is based on, but modified from, the behavior of an existing class.
  • If we define a class Ruby that extends a class Gem, we say that Ruby is a subclass of Gem, and that Gem is the superclass of Ruby.
  • If you do not specify a superclass when you define a class, then your class implicitly extends Object.
• extend: extend(module, ...) → obj
  • Just mix the instance methods from each of the given modules in to obj.
• include: include(module, ...) → self
  • Invokes Module.append_features on each parameter in reverse order.
  • The module that you include is effectively added as a superclass of the class
    being defined.
  • It’s as if the module is the parent of the class that it is
    mixed into.
• prepend: prepend(module, ...) → self
  • Invokes Module.prepend_features on each parameter in reverse order.
  • Ruby 2 introduced the prepend method.
  • Logically, this behaves just like include, but the methods in the prepended module take precedence over those in the host class. Ruby pulls off this magic by inserting a dummy class in
    place of the original host class and then inserting the prepended module between the two.