From: Rick DeNatale <rick.denatale@...>
Date: 2007-10-22T23:45:45+09:00
Subject: Re: Conflicts between using respond_to? and extending Ruby

On 10/22/07, David A. Black <dblack@wobblini.net> wrote:

> On Mon, 22 Oct 2007, Trans wrote:

> > I recently cam across an interesting conflict between open-uri.rb and
> > Facets rendition of kernel/metaid.rb. Facets defines a general
> > extension Kernel#meta, and open-uri defines OpenURI::Meta#meta. open-
> > uri uses OpenURI::Meta to extend StringIO via singleton. This is all
> > fine, but then open-uri checks to see if a StringIO object has been
> > extended by doing:
> >
> >  io.respond_to? :meta
> >
> > And that's where the problem lies, b/c if you've loaded 'facets/kernel/
> > metaid' you're going to get a false positive here. Now the best remedy
> > is open-uri to be more precise:
> >
> >  io.is_a? OpenURI::Meta
> >
> > That fixes the the problem. But it raises an interesting question.
> > I've used #respond_to? myself from time to time thinking it was oh, so
> > duck-type kosher; never realizing that it might clash with general
> > extensions.
> >
> > So where lies the fault in this conflict? Are extensions the bad guy,
> > or is respond_to? really not a good oop concept? Or..?
>
> I think this is just the age-old issue about adding methods to
> existing classes and hitting conflicts. #respond_to? is relatively
> dumb; it can't tell you what the method actually does. I think of it
> as an important tool for "soft" duck typing, in contrast with "hard"
> duck typing where you just send the object the message.

Okay, I'm claiming stake to coining what I hope becomes as much of a
meme as duck typing:

http://talklikeaduck.denhaven2.com/articles/2007/10/22/chicken-typing-isnt-duck-typing


-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/