From: "fxn (Xavier Noria)" <fxn@...>
Date: 2012-07-29T21:38:09+09:00
Subject: [ruby-core:46855] [ruby-trunk - Bug #6810] `module A::B; end` is not equivalent to `module A; module B; end; end` with respect to constant lookup (scope)


Issue #6810 has been updated by fxn (Xavier Noria).


They are very decoupled, name is the only bit mostly in common, set on constant assignment. May I link to a talk of mine, which covers this (content constrained by the 30min slot): http://www.youtube.com/watch?v=wCyTRdtKm98.

In particular, the name of the modules is unrelated to the constants they are stored in. See for example

    module M
    end

    N = M

    module A
      B = M
    end

Now, the module object that is *stored* in the constant M, it is also stored in the constant N, and in the constant A::B. It can be stored in a hundred places. And the constant M can disappear:

    Object.instance_eval { remove_const(:M) }

So that module object whose name is "M" is well and alive. You can reopen, mixin the module... everything. The constant M is no longer available, but that is irrelevant as far as Ruby is concerned. Modules are objects, constants just storage, formally they are very superficially related to each other, although in practice we often identify them of course.
----------------------------------------
Bug #6810: `module A::B; end` is not equivalent to `module A; module B; end; end` with respect to constant lookup (scope)
https://bugs.ruby-lang.org/issues/6810#change-28530

Author: alexeymuranov (Alexey Muranov)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 
ruby -v: ruby 1.9.3p194 (2012-04-20 revision 35410) [x86_64-darwin10.8.0]


=begin
Is this the expected behavior?  To me it is rather surprising:

 N = 0

 module A
   module B
     def self.f; N; end
   end
   N = 1
 end

 A::B.f # => 1

but

 N = 0

 module A; end

 module A::B
   def self.f; N; end
 end

 module A
   N = 1
 end

 A::B.f # => 0

Even more striking:

 module A
   module B
     def self.f; N; end
   end
 end

 N = 0

 A::B.f # => 0

 A::N = 1

 puts A::B.f # => 1

 A::B::N = 2

 A::B.f # => 2

but

 module A; end

 module A::B
   def self.f; N; end
 end

 N = 0

 A::B.f # => 0

 A::N = 1

 A::B.f # => 0

 A::B::N = 2

 A::B.f # => 2


=end


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