Object/Class in Ruby

[dylanninin]

Bootstraps the class hierarchy

 //ruby/object.c
 *  Document-class: Class
 *
 *  Classes in Ruby are first-class objects---each is an instance of
 *  class <code>Class</code>.
 *
 *  Typically, you create a new class by using:
 *
 *    class Name
 *     # some code describing the class behavior
 *    end
 *
 *  When a new class is created, an object of type Class is initialized and
 *  assigned to a global constant (<code>Name</code> in this case).
 *
 * 
 * Classes, modules, and objects are interrelated. In the diagram
 *  that follows, the vertical arrows represent inheritance, and the
 *  parentheses metaclasses. All metaclasses are instances
 *  of the class `Class'.
 *
 * Initializes the world of objects and classes.
 *
 * At first, the function bootstraps the class hierarchy.
 * It initializes the most fundamental classes and their metaclasses.
 * - \c BasicObject
 * - \c Object
 * - \c Module
 * - \c Class
 * After the bootstrap step, the class hierarchy becomes as the following
 * diagram.
 *                             +---------+             +-...
 *                             |         |             |
 *             BasicObject-----|-->(BasicObject)-------|-...
 *                 ^           |         ^             |
 *                 |           |         |             |
 *              Object---------|----->(Object)---------|-...
 *                 ^           |         ^             |
 *                 |           |         |             |
 *                 +-------+   |         +--------+    |
 *                 |       |   |         |        |    |
 *                 |    Module-|---------|--->(Module)-|-...
 *                 |       ^   |         |        ^    |
 *                 |       |   |         |        |    |
 *                 |     Class-|---------|---->(Class)-|-...
 *                 |       ^   |         |        ^    |
 *                 |       +---+         |        +----+
 *                 |                     |
 *    obj--->OtherClass---------->(OtherClass)-----------...
 *
 * Then, the function defines classes, modules and methods as usual.
 * \ingroup class

Document-class: BasicObject

 //ruby/object.c
 *
 *  BasicObject is the parent class of all classes in Ruby.  It's an explicit
 *  blank class.
 *
 *  BasicObject can be used for creating object hierarchies independent of
 *  Ruby's object hierarchy, proxy objects like the Delegator class, or other
 *  uses where namespace pollution from Ruby's methods and classes must be
 *  avoided.
 *
 *  To avoid polluting BasicObject for other users an appropriately named
 *  subclass of BasicObject should be created instead of directly modifying
 *  BasicObject:
 *
 *    class MyObjectSystem < BasicObject
 *    end
 *
 *  BasicObject does not include Kernel (for methods like +puts+) and
 *  BasicObject is outside of the namespace of the standard library so common
 *  classes will not be found without using a full class path.
 *
 *  A variety of strategies can be used to provide useful portions of the
 *  standard library to subclasses of BasicObject.  A subclass could
 *  <code>include Kernel</code> to obtain +puts+, +exit+, etc.  A custom
 *  Kernel-like module could be created and included or delegation can be used
 *  via #method_missing:
 *
 *    class MyObjectSystem < BasicObject
 *      DELEGATE = [:puts, :p]
 *
 *      def method_missing(name, *args, &block)
 *        super unless DELEGATE.include? name
 *        ::Kernel.send(name, *args, &block)
 *      end
 *
 *      def respond_to_missing?(name, include_private = false)
 *        DELEGATE.include?(name) or super
 *      end
 *    end
 *
 *  Access to classes and modules from the Ruby standard library can be
 *  obtained in a BasicObject subclass by referencing the desired constant
 *  from the root like <code>::File</code> or <code>::Enumerator</code>.
 *  Like #method_missing, #const_missing can be used to delegate constant
 *  lookup to +Object+:
 *
 *    class MyObjectSystem < BasicObject
 *      def self.const_missing(name)
 *        ::Object.const_get(name)
 *      end
 *    end
 *

Document-class: Object

 //ruby/object.c
 *  Object is the default root of all Ruby objects.  Object inherits from
 *  BasicObject which allows creating alternate object hierarchies.  Methods
 *  on Object are available to all classes unless explicitly overridden.
 *
 *  Object mixes in the Kernel module, making the built-in kernel functions
 *  globally accessible.  Although the instance methods of Object are defined
 *  by the Kernel module, we have chosen to document them here for clarity.
 *
 *  When referencing constants in classes inheriting from Object you do not
 *  need to use the full namespace.  For example, referencing +File+ inside
 *  +YourClass+ will find the top-level File class.
 *
 *  In the descriptions of Object's methods, the parameter <i>symbol</i> refers
 *  to a symbol, which is either a quoted string or a Symbol (such as
 *  <code>:name</code>).
 */

Document-class: Kernel

//ruby/object.c
*
* The Kernel module is included by class Object, so its methods are
* available in every Ruby object.
*
* The Kernel instance methods are documented in class Object while the
* module methods are documented here.  These methods are called without a
* receiver and thus can be called in functional form:
*
*   sprintf "%.1f", 1.234 #=> "1.2"
*
*
rb_mKernel = rb_define_module("Kernel");
rb_include_module(rb_cObject, rb_mKernel);

Document-class: Module

A Module is a collection of methods and constants. The methods in a module may be instance methods or module methods. Instance methods appear as methods in a class when the module is included, module methods do not. Conversely, module methods may be called without creating an encapsulating object, while instance methods may not.

In the descriptions that follow, the parameter sym refers to a symbol, which is either a quoted string or a Symbol (such as :name).

module Mod
  include Math
  CONST = 1
  def meth
    #  ...
  end
end
Mod.class              #=> Module
Mod.constants          #=> [:CONST, :PI, :E]
Mod.instance_methods   #=> [:meth]

Init class hierarchy

//ruby/class.c
void
Init_class_hierarchy(void)
{
    rb_cBasicObject = boot_defclass("BasicObject", 0);
    rb_cObject = boot_defclass("Object", rb_cBasicObject);
    rb_gc_register_mark_object(rb_cObject);

    /* resolve class name ASAP for order-independence */
    rb_class_name(rb_cObject);

    rb_cModule = boot_defclass("Module", rb_cObject);
    rb_cClass =  boot_defclass("Class",  rb_cModule);

    rb_const_set(rb_cObject, rb_intern_const("BasicObject"), rb_cBasicObject);
    RBASIC_SET_CLASS(rb_cClass, rb_cClass);
    RBASIC_SET_CLASS(rb_cModule, rb_cClass);
    RBASIC_SET_CLASS(rb_cObject, rb_cClass);
    RBASIC_SET_CLASS(rb_cBasicObject, rb_cClass);
}

[dylanninin]

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.