From: Xavier Noria <fxn@...>
Date: 2007-11-11T21:43:07+09:00
Subject: about const_missing

Active Support has this code (edited for brevity):

   # dependencies.rb ------------------------------------
   class Module #:nodoc:
     def const_missing(class_id)
       Dependencies.load_missing_constant self, class_id
     end
   end

   class Class
     def const_missing(class_id)
       if [Object, Kernel].include?(self) || parent == self
         super
       else
         ...
       end
     end
   end

   # intropection.rb ------------------------------------
   class Module
     def parent
       parent_name = name.split('::')[0..-2] * '::'
       parent_name.empty? ? Object : parent_name.constantize
     end
   end

Looks like the condition "[Object, Kernel].include?(self) || parent ==  
self" wants to test whether this is a root class, but no matter which  
is the intention I wonder:

   (1) Since Kernel is a module, is there any chance that self
       in Class#const_missing is Kernel?

   (2) Can parent == self be true with self != Object?

For (2) I've even tried to contrived things like

   class A
     A = A
   end

that makes A::A == A but has not been able to fool Module#parent. I  
think "parent == self" is redundant but since it is there I want to be  
sure I don't miss some edge case.

-- fxn