From: Jim Freeze <jim@...>
Date: 2002-09-19T22:20:34+09:00
Subject: Re: Is better to subclass or to add methods to an existing class?

On Thu, Sep 19, 2002 at 09:20:13PM +0900, Vincent Foley wrote:
> 
> But my friend told me that Python didn't have that because it was not a
> good thing and it was not the proper way to do it.  He said that the
> true way of doing it, is to subclass (since Python 2.2 can now subclass
> builtin types) the base class:
> 
[snippage]
> 
> His main argument was just that, "It's the Wrong Way (TM) to do it".  To
> me, it just seems like extra code and added complexity.
> 
> Can you enligthen me and tell me if it's really that bad an idea to add
> methods to an existing class, or if he's just being a Python zealot?
> 

I think it could be considered bad because it can produce
alergic reactions between libraries.

For example:

--- LibA
class String
  def rot13
    tr(A-Za-z,...)
  end
end

--- LibB
class String
  def rot13
    puts "rotate 13 degrees"
  end
end

----

require liba
require libb

"fred".rot13  #=>  this will probably not do what you want it to.

Since both libraries have redefined a core class and have added
a method with the same name, there will ultimately be a problem
in the code.

This is why I avoid modifying core libraries and I hope other
library writers do as well.


-- 
Jim Freeze
----------
Programming Ruby 
 def initialize; fun; end
A language with class