# Programming Ruby ### The Pragmatic Programmer's Guide
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class Class |
Parent: | Module
Version: | 1.6

### Index:

inherited new new superclass

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

class methods
inherited | aClass.inherited( aSubClass )
|  | This is a singleton method (per class) invoked by Ruby when a subclass of aClass is created. The new subclass is passed as a parameter.

    class Top
      def Top.inherited(sub)
        print "New subclass: ", sub, "\n"
      end
    end

    class Middle < Top
    end

    class Bottom < Middle
    end
produces:
    New subclass: Middle
    New subclass: Bottom
new | Class.new( aSuperClass=`Object` ) -> aClass
|  | Creates a new anonymous (unnamed) class with the given superclass (or `Object` if no parameter is given).

instance methods
new | aClass.new( [ args ]* ) -> anObject
|  | Creates a new object of aClass's class, then invokes that object's `initialize` method, passing it args.
superclass | aClass.superclass -> aSuperClass or `nil`
|  | Returns the superclass of aClass, or `nil`.
`Class.superclass` | » | `Module`
`Object.superclass` | » | `nil`

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Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
Copyright © 2001 by Addison Wesley Longman, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at http://www.opencontent.org/openpub/)).

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