From: Gavin Kistner <gavin@...>
Date: 2005-05-17T13:10:19+09:00
Subject: Extending an Instance only Once

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I have a method that requires that the arguments passed to it have  
been in-mixed with a module. Currently, my code looks like this:

def my_method( the_obj )
     the_obj.extend( MyModule ) unless the_obj.inherits_from? 
( MyModule )
end

class Object
     def selfclass
         class << self; self; end
     end

     # Return true if the instance inherits from the supplied  
_class_or_module_.
     def inherits_from?( class_or_module )
         self.class.ancestors.include?( class_or_module ) or  
self.selfclass.ancestors.include?( class_or_module )
     end
end


Is there a better way to do that? (I'm testing if the object inherits  
from a class which was extended by the module, OR if the instance  
itself was already extended.) Does it end up being cheaper/faster to  
just always re-extend the instance? (What happens if you extend both  
the class and an instance of that class? Does the singleton class  
take precedence?)

--
"When I am working on a problem I never think about beauty. I only  
think about how to solve the problem. But when I have finished, if  
the solution is not beautiful, I know it is wrong."
- R. Buckminster Fuller


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