From: Xavier Noria <fxn@...>
Date: 2007-11-16T17:49:30+09:00
Subject: constant name resolution and module_eval

I'm trying to understand well the rules for constant name resolution.  
By now what I have is:

   (1) A constant is first looked up in the current module,
   then recursively in its mixins (ancestors). Then go up
   to the parent, and iterate up to the mixins of Object.

   (2) When you resolve a relative path Foo::Bar first you
   resolve the constant Foo using the rule above. If found,
   you look for Bar in Foo. There's no backtracking if that
   choice for Foo fails.

If that's right, I need yet to refine what's the "current module".  
 From my trials looks like the current module is determined by "module/ 
class" explicit keyword nesting, and module_eval does not change it:

   C = "Object"

   module M
     C = "M"
   end

   M.module_eval do
     def self.const; C end
     D = 1
   end

   puts M.const
   puts M::D # -> NameError

But surprisingly module_eval defines M.const, and does _not_ define  
M::D. I know module_eval sees the surrounding scope and that allows  
some idioms a regular module reopening does not, but I need yet to put  
the pieces together for constants.

Is that there are two kinds of "current module"s, one for constant  
lookup, and another one for method definitions, which happen to match  
when you use the "module/class" keyword nesting? My trials suggest  
that's the case but I'd like someone with a better understanding of  
Ruby internals to confirm it and perhaps define more clearly those two  
"current" modules at any given point of the program.

-- fxn