From: Robert Klemme <shortcutter@...>
Date: 2009-12-30T18:34:16+09:00
Subject: Re: Using #include at the instance level?

--0016e6d77e322d0f67047beed76b
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

2009/12/30 fkocherga <fkocherga@gmail.com>:
>>
>> AFAIK it hasn't changed and your code could never work in any version
>> of Ruby because the const lookup in method #n is done _statically_.
>
> But it should not, consider:
>
> module M
> =A0module N
> =A0end
> end
>
> #Class.new do <---- This does not work in 1.8.7!
> class B < Object
> =A0include M
> =A0N
> end
>
> When 'class B < Object' replaced with 'Class.new do' the Ruby 1.8.7 inter=
preter complains about uninitialized constant N. What is the big reason for=
 dynamically defined class to behave so differently? It would be very non o=
bvious and unexpected behavior. Actually both cases work as expected in Rub=
y 1.9.1 and this is correct behavior according to the Ruby Draft.

Thanks for the test case!  It never occurred to me to do a const
lookup in a class defined with a class body so I never stumbled across
this.  I did a bit of research and this is what I found:

Statement from Matz about the change: "In 1.8, constant uses lexical
look-up, even within the block given to instance_eval().  We changed
this behavior in 1.9 to simplify things."
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/181646

Found via http://eigenclass.org/hiki/withdrawn-experimental-ruby-features
- I am not so sure about the "experimental" status of this though -
maybe this is due to the last update date of the page in 2007...

Adam Gardner also made an interesting observation about the difference
between const_get and direct constant lookup:
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/333677
(I have changed the test output to easier interpret it. See attachment.)

There's also this discussion
http://blade.nagaokaut.ac.jp/cgi-bin/vframe.rb/ruby/ruby-core/25865?25832-2=
6487

And this
http://blade.nagaokaut.ac.jp/cgi-bin/vframe.rb/ruby/ruby-talk/334016?333995=
-335445

To sum it up: Ruby 1.9 changed lookup rules from lexical (aka static)
to dynamic.  IMHO this explains the observed different behavior.
Thanks again for poking.

Kind regards

robert

--=20
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

--0016e6d77e322d0f67047beed76b
Content-Type: application/octet-stream; name="const-lookup-2.rb"
Content-Disposition: attachment; filename="const-lookup-2.rb"
Content-Transfer-Encoding: base64
X-Attachment-Id: f_g3twgwmm0
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=
--0016e6d77e322d0f67047beed76b--