From: "David A. Black" <dblack@...>
Date: 2009-01-03T01:30:43+09:00
Subject: Re: What does 'Monkey Patching' exactly Mean in Ruby?

Hi --

On Sat, 3 Jan 2009, Robert Dober wrote:

> On Fri, Jan 2, 2009 at 1:42 PM, David A. Black <dblack@rubypal.com> wrote:
>
>> 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 = "abc".extend(MyGsubBang)
> This indeed is a very sensible and elegant way to do things.
>
> The true werewolf of dynamic extension (I am happy with MP but there
> seems to be a consensus against that term...) however is this case
>
> # first I am using what I have just learned from David :-P
> module VersionIndependentInstanceMethods
>   def instance_methos *args, &blk
>      super.map{ |mn| mn.to_sym }
>   end
> end
> Class.include Version...

I'd be careful there. You're making a class-wide (all instances of
Class) change. (include is private, but still :-) That could bite you
if you're depending on instance_methods to return strings, which we
can legitimately do in 1.8.

> class WhatEverOrMaybeEvenACoreClass
>   if instance_methods.include? :xxx then
>     raise IDoNotKnowWhatToDoError, "No I really don't"
>   else
>     def xxx ....
>     end
>  end
> end
>
> Any insights on IDoNotKnowWhatToDoError?

I guess you could go back to the #extend technique. I should add,
however, that even that technique isn't bullet-proof. object#a might
call object#b, so if you override object#b in a module, object#a won't
get the behavior it expects.


David

-- 
David A. Black / Ruby Power and Light, LLC
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