From: Robert Klemme <shortcutter@...>
Date: 2009-04-07T16:49:11+09:00
Subject: Re: class C < B < A

On 07.04.2009 00:41, Iñaki Baz Castillo wrote:
> El Martes 07 Abril 2009, Joel VanderWerf escribió:
>> Iñaki Baz Castillo wrote:
>>> Hi, I have this case:
>>>
>>>   class A     ; end
>>>   class B < A ; end
>>>   class C < B ; end
>>>
>>>   a = A.new
>>>   b = B.new
>>>   c = C.new
>>>
>>>
>>> I look for a way (***) to get the following results:
>> ...
>>
>> #instance_of? works for all cases except:
>>>   c *** B => true
>> Are you sure you need this to be true?
> 
> Yes. Basically A is String and B is a child of String with various methods, 
> and C is a more specific class.

Frankly, I find this a bit spooky for several reasons: first, you 
inherit String which IMHO is almost always a bad idea(tm).  You should 
consider using delegation, so you have

class B
   attr_reader :str
end

class C < B; end

Then, you introduce inconsistencies in inheritance checking.  That might 
yield all sorts of surprises.

If you want to do it nevertheless, I'd probably go for a special method 
which you override appropriately:

class Module
   def class_of?(obj)
     if self == String
       self == obj.class
     else
       self === obj
     end
   end
end

class B < String
end

class C < B
end

classes = [String,B,C]
classes.each do |cl|
   puts cl
   o = cl.new

   classes.each do |cl2|
     print cl2, " ", cl2.class_of?(o), "\n"
   end

   puts "--"
end


Something along these lines.

Kind regards

	robert