From: "David A. Black" <dblack@...>
Date: 2007-11-09T08:32:59+09:00
Subject: Re: 'Class.inherited' v. 'inherited' syntax inside Class

Hi --

On Fri, 9 Nov 2007, 7stud -- wrote:

> How come when you redefine the inherited method in Class, you don't use
> the 'class method' syntax?  This doesn't work:
>
> class Class
>  def Class.inherited(class_obj)
>    puts class_obj
>    puts
>  end
> end
>
>
> Instead, you have to write:
>
> class Class
>  def inherited(class_obj)
>    puts class_obj
>    puts
>
>  end
> end
>
> Yet, in pickaxe2 on p. 445, the book lists inherited as a class method
> of Class.

The term "class method" can refer to either of two things: an instance
method of Class, or a singleton method of a given class. When you call
them, the technique is the same:

   class Class
     def an_instance_method
       puts "I'm an instance method of Class"
     end
   end

   class C
     def a_singleton_method
       puts "I'm a singleton method of C"
     end
   end

   C.an_instance_method
   C.a_singleton_method

So... when you do this:

   class Class
     def inherited ...

you're defining an instance method called "inherited", and all
instances of Class -- that is, all classes -- will have that method.

When you define Class.inherited, you're defining a singleton method on
Class. The only thing that would be affected by that would be if you
created a subclass of Class -- but Ruby doesn't permit that.


David

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