Ruby 1.9.2 Constant Lookup with BasicObject

ruby-1.9.2-p0 > module M
ruby-1.9.2-p0 ?> end
=> nil
ruby-1.9.2-p0 > class X < BasicObject
ruby-1.9.2-p0 ?> include M
ruby-1.9.2-p0 ?> end
NameError: uninitialized constant X::M
from (irb):4:in <class:X>' from (irb):3 from /home/trans/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in

module M is defined inside Object space.
X is one level above it - it is inside BasicObject( where no Object
space is visible)
Inside X you try to include an object from other space (one level below)
I think it will work if you include Object::M

On Aug 31, 8:50 am, Eugen C. [email protected] wrote:

=> nil
ruby-1.9.2-p0> class X< BasicObject
ruby-1.9.2-p0 ?> include M
ruby-1.9.2-p0 ?> end
NameError: uninitialized constant X::M
from (irb):4:in <class:X>' from (irb):3 from /home/trans/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in

I filed a bug report on Ruby’s issue tracker and matz brought up the
same. Here’s my take:

I see the technical reason it occurs, but to accept that as proper
behavior is going to hobble the usefulness of BasicObject.

First of all, it means one’s ability to open a class and modify it
will be conditional. One will have to check if it is a BasicObject
upfront. That’s easy to do if you’re working with one class you
already know, but consider how it effects doing some meta-programming
where code is injected into any arbitrary class.

Worst still is that it makes importing code into a namespace very
fragile. Consider the simplistic example of having some code in a
script to eval into a module.

module M
eval(File.read(‘file.rb’))
end

If file.rb contains:

class R
end

class Q < BasicObject
def r; R.new; end
end

Then it will break whether we use R or ::R.

I feel the underlying issue here goes back to some other issues we’ve
discussed some years ago about the top-level. Routing the toplevel to
Object is not as flexible or robust as having a toplevel be an
independent self-extended module in which constant resolution would
terminate.

The rules of constant name resolution have changed with BasicObject.
There was a step before that said that if nesting and ancestors didn’t
find it, you checked Object.

I’d like to know the current complete algorithm, including const_missing
calls.

Hi,

I understand your complain. But the solution should be concrete, and
hopefully consistent with other parts of the language. I am not sure
your “a toplevel being an independent self-extended module” proposal
is the way to go (yet).

          matz.

In message “Re: Ruby 1.9.2 Constant Lookup with BasicObject”
on Tue, 31 Aug 2010 23:23:53 +0900, Intransition
[email protected] writes:
|
|On Aug 31, 8:50 am, Eugen C. [email protected] wrote:
|> module M is defined inside Object space.
|> X is one level above it - it is inside BasicObject( where no Object
|> space is visible)
|> Inside X you try to include an object from other space (one level below)
|> I think it will work if you include Object::M
|>
|> On 08/30/2010 07:47 PM, Intransition wrote:
|>
|> > ruby-1.9.2-p0> module M
|> > ruby-1.9.2-p0 ?> end
|> > => nil
|> > ruby-1.9.2-p0> class X< BasicObject
|> > ruby-1.9.2-p0 ?> include M
|> > ruby-1.9.2-p0 ?> end
|> > NameError: uninitialized constant X::M
|> > from (irb):4:in <class:X>' |> > from (irb):3 |> > from /home/trans/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in
|
|I filed a bug report on Ruby’s issue tracker and matz brought up the
|same. Here’s my take:
|
|I see the technical reason it occurs, but to accept that as proper
|behavior is going to hobble the usefulness of BasicObject.
|
|First of all, it means one’s ability to open a class and modify it
|will be conditional. One will have to check if it is a BasicObject
|upfront. That’s easy to do if you’re working with one class you
|already know, but consider how it effects doing some meta-programming
|where code is injected into any arbitrary class.
|
|Worst still is that it makes importing code into a namespace very
|fragile. Consider the simplistic example of having some code in a
|script to eval into a module.
|
| module M
| eval(File.read(‘file.rb’))
| end
|
|If file.rb contains:
|
| class R
| end
|
| class Q < BasicObject
| def r; R.new; end
| end
|
|Then it will break whether we use R or ::R.
|
|I feel the underlying issue here goes back to some other issues we’ve
|discussed some years ago about the top-level. Routing the toplevel to
|Object is not as flexible or robust as having a toplevel be an
|independent self-extended module in which constant resolution would
|terminate.

After some trial and error it seems the algorithm is the same as in
1.8 if we take into account that the special rule that checks Object
as a last resort applies only to modules.

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