Class

Classes in Ruby are first-class objects—each is an instance of class Class.

When a new class is created (typically using class Name … end), an object of type Class is created and assigned to a global constant (Name in this case). When Name.new is called to create a new object, the new method in Class is run by default. This can be demonstrated by overriding new in Class:

class Class
   alias oldNew  new
   def new(*args)
     print "Creating a new ", self.name, "\n"
     oldNew(*args)
   end
 end

 class Name
 end

 n = Name.new

produces:

Creating a new Name

Classes, modules, and objects are interrelated. In the diagram that follows, the vertical arrows represent inheritance, and the parentheses meta-classes. All metaclasses are instances of the class `Class’.

                     +-----------------+
                    |                  |
   BasicObject-->(BasicObject)         |
        ^           ^                  |
        |           |                  |
      Object---->(Object)              |
       ^  ^        ^  ^                |
       |  |        |  |                |
       |  |  +-----+  +---------+      |
       |  |  |                  |      |
       |  +-----------+         |      |
       |     |        |         |      |
+------+     |     Module--->(Module)  |
|            |        ^         ^      |

OtherClass–>(OtherClass) | | |

  |         |      |
Class---->(Class)  |
  ^                |
  |                |
  +----------------+