From: ts <decoux@...>
Date: 2002-02-05T00:04:57+09:00
Subject: Re: Mixins and accessing earlier definitions.

>>>>> "H" == Hugh Sasse Staff Elec Eng <hgs@dmu.ac.uk> writes:

H> subclass in between including successive modules.  I think this is
H> because included modules appear as superclasses of the class that
H> includes them.

 Yes, this is something like this. For example with

  class A end

 the inheritance of A is

   A < Object 

 Now if you include the module B, this will give

   class A; include B; end

   A < [B] < Object

 [B] is a proxy class to the module B

 When an object of A call a method, ruby will look in A, then B, etc

H> If a module is intended to {override or add} a method, how should this
H> be done in idiomatic Ruby? Obviously my way of thinkig is wrong :-).
H> I think using alias in the case where a method is added could be a
H> problem, because the old method to be aliased will not exist.

 Well, you don't have this problem with 'include', for example if you want
 to redefine a method of Object (like to_s) for A, but using a module you
 just write 

   module B
      def to_s
         "B::" + super
      end
   end
   class A
      include B
   end

   A.new.to_s

 When #to_s is invoked, ruby first search in A, then in B where it find it
 The call to #super in B, will force ruby to continue the search and call
 the original method of Object
    
H> Also, several successive overrides could be a problem using alias.

 It's best to test if a method exist before trying to define un alias,
 otherwise you can create infinite loop.



Guy Decoux