From: "David A. Black" <dblack@...>
Date: 2009-01-02T21:42:16+09:00
Subject: Re: What does 'Monkey Patching' exactly Mean in Ruby?

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Hi --

On Fri, 2 Jan 2009, J=F6rg W Mittag wrote:

> Phlip wrote:
>> Yaser Sulaiman wrote:
>>> 3- Is the following considered as monkey patching, or is it something e=
lse?
>>>
>>> class String
>>>   def foo
>>>     "bar"
>>>   end
>>> end
>>
>> No, that is simply extending the class with a new method.
>
> Ah, but that's the interesting part: how do you know that somebody
> else didn't already add a String#foo method? In that case, it *would*
> be monkey patching. Even worse: which of the two methods would be
> considered monkey patching and which one wouldn't, would depend
> entirely on the *load order* of those two snippets of code.
>
> That's why I don't think distinguishing between adding and changing
> methods makes sense: either both are monkey patching or neither are.

This was true, and quite deeply examined, well before the term "monkey
patching" came along to cloud the issue :-)

Adding a new method involves a kind of Prisoners' Dilemma, situation,
where if either of us is the only one to add that particular method,
we "win", but if we both do it, we lose. Changing methods, however,
can be done in a relatively low-impact way, if you chain them rather
than really changing them.

I'll put in a plug for what I believe is by far the safest way to
extend core functionality, namely #extend.  A classic case is the
desire to have #gsub! not return nil when the string doesn't change.

   module MyGsubBang
     def gsub!(*args, &block)
       super(*args, &block) || self
     end
   end

   str =3D "abc".extend(MyGsubBang)

Among other advantages, this way of doing it forces you to think
carefully about the specific objects, and not throw too large a
blanket over what is actually a tiny problem (having one or two
objects that you want to behave different from the norm).


David

--=20
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Coming in 2009: The Well-Grounded Rubyist (http://manning.com/black2)

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