From: Christoph <chr_news@...>
Date: 2003-01-04T04:54:24+09:00
Subject: Re: toplevel modules and classes

"Eugene Scripnik" <Eugene.Scripnik@itgrp.net> wrote
....
> Well, I just wanted to build classes/modules tree of my application.
> This structure is so complicated. And I wanted to do it in generalized
> way and also was surprised when I put another class/module into class
> and compiler found it OK.
> So, both module and class accept defining modules and classes inside
> them, but Class#constants and Module#constants behave in different
> way. That was second surprise.

There is instance_method and a singleton_method (class_method)
of the class "Module"  called  `constant' .
---
class Module
 p singleton_methods.include?('constants') # true
end

class Module
  p instance_methods.include?('constants') # true
end
---

The singleton version calculates the current visible constants - this
depends
on the current binding - here is an old example  illustrating the difference
between Object.constants (calling the instance version) and Module.constants
(Class.instance would work too) calling the singleton version.

---
def minus (bind)
  puts eval('Module.constants - Object.constants',bind).sort.join(', ')
end

A0 = 1
module A
   B = 'B'
   class C
   D = 'D'
  end
  class E
    F = 'F'
  end
end

minus binding        # =>
module A
   minus  binding    # => B, C, E
   class C
      minus  binding # => B, C, D, E
   end
   class E
      minus binding  # => B, C, D, F
   end
end
---


/Christoph