Roel Wuyts wrote:
> Andreas, I prefer refactoring, but refactoring assumes a closed world 
> approach where you control all the pieces of the puzzle.

I would call access to all pieces of the puzzle "open" not "closed" but 
be that as it may...

> It simply is not always possible to refactor (because you do not have 
> the source, because you do not want to create a fork, because you have 
> other programs that absolutely rely on the old behaviour, etc.). In that 
> case extending the existing software from within your own package helps, 
> but should be used sparingly for all the reasons you mention.
> 
> Note that a decent module system should support both.

Which I have advocated earlier myself. I have never doubted that there 
are situation in which patching another module is advantageous and 
desirable. Which is why I don't understand why some people are so 
opposed to the idea of having the other end of the spectrum (isolation) 
available as well.

Cheers,
   - Andreas