From: Peter McLain <peter.mclain@...>
Date: 2010-03-05T04:31:39+09:00
Subject: [ruby-core:28482] Question on scoped constant resolution Class vs Module

I asked this on ruby-talk, but didn't get anywhere.  Someone suggested  
I post over here.

Resolution of fully scoped constants behaves differently if there is a  
class versus a module in the name:

   XYZ = 10

   module M
   end

   class C
   end

   p defined? M::XYZ  # => nil
   p defined? C::XYZ  # => "constant"

A few questions:

1: Is this difference intended?
2: If so, what is the rationale?
3: Should defined?(C::XYZ) behave differently than C.const_defined? 
(:XYZ) ?
4: Is the draft ruby spec correct, or MRI behavior correct, or did I  
miss something in the following:

I think the behavior with M::XYZ does not conform to section 11.4.3.2  
of the draft ruby spec:

11.4.3.2
  (a) the primary-expression is M,
  (b) M is a module, do not raise TypeError
  (c 1) XYZ is the constant-identifier
  (c 2) XYZ is not one of the constants defined in M
  (c 3 i) There are no included modules in M (skip)
  (c 3 ii) N/A
  (c 3 iii) Goto step e of section 11.4.3.1

11.4.3.1
  (e) M is not a class
  (e 1) Search Object for a binding for XYZ

So, according to the spec, it looks like M:XYZ should resolve to the  
XYZ in Object and MRI is incorrect to return nil.

Did I miss something?


The real world occurrence of this was:

    return unless defined? RDoc::VERSION # RDoc 1 does not have VERSION
    # code that blows up if RDoc 1 being used...

Which does not currently work in MagLev, since MagLev returns  
"constant" for defined?RDoc::VERSION.  One could argue that the proper  
test, which works for both classes and modules in all ruby  
implementations, is:

    return unless RDoc.const_defined? :VERSION

--  
Peter McLain
peter.mclain@gemstone.com