From: Robert Klemme <shortcutter@...>
Date: 2009-08-18T20:46:58+09:00
Subject: Re: Including a module in an included module.

2009/8/18 Prince Nez <prince.nez@gmail.com>:
>    module M1; end
>    module M2; include M1; end
>    module M1; DOG = :woof; end
>    module M2; DOG; end
>    # => :woof
>
> I can add to a module after it has been included. Neat.
>
>    module M1; DOG = :woof; end
>    module M2; include M1; end
>    module M3; include M2; end
>    module M3; DOG; end
>    # => :woof
>
> Including a module seems to give me any modules that it includes. Swish.
>
>    module M2; end
>    module M3; include M2; end
>    module M1; DOG = :woof; end
>    module M2; include M1; end
>    module M3; DOG; end
>    # => NameError: uninitialized constant M3::DOG
>
> So I assumed I'd be able to include a module in a module after it has
> been included, if you get my drift. It surprises me that this dog
> doesn't bark.

Inclusion apparently works by extracting the ancestors of a module at
inclusion time and placing them in the ancestor chain of the class:

irb(main):001:0> module A
irb(main):002:1> def foo; "foo"; end
irb(main):003:1> end
=> nil
irb(main):004:0> A.ancestors
=> [A]
irb(main):005:0> class C
irb(main):006:1> include A
irb(main):007:1> end
=> C
irb(main):008:0> C.ancestors
=> [C, A, Object, Kernel, BasicObject]
irb(main):009:0> C.new.foo
=> "foo"
irb(main):010:0> module B
irb(main):011:1> def bar; "bar"; end
irb(main):012:1> end
=> nil
irb(main):013:0> module A
irb(main):014:1> include B
irb(main):015:1> end
=> A
irb(main):016:0> A.ancestors
=> [A, B]
irb(main):017:0> C.ancestors
=> [C, A, Object, Kernel, BasicObject]
irb(main):018:0> C.new.bar
NoMethodError: undefined method `bar' for #<C:0x100de5c0>
        from (irb):18
        from /opt/bin/irb19:12:in `<main>'
irb(main):019:0> class C
irb(main):020:1> include A
irb(main):021:1> end
=> C
irb(main):022:0> C.ancestors
=> [C, A, B, Object, Kernel, BasicObject]
irb(main):023:0> C.new.bar
=> "bar"
irb(main):024:0>

As you can see, you can fix that by reincluding the module.

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/