From: Robert Klemme <shortcutter@...>
Date: 2010-06-07T18:34:39+09:00
Subject: Re: Singleton classes and Namespce

2010/6/6 Intransition <transfire@gmail.com>:
> Do singleton classes not get the same namespace treatment as normal
> classes?

I think so.

>  module M
>    class X; end
>  end
>
>  o = Object.new
>  => #<Object:0x7fc61f1a1e58>
>
>  (class << o; self; end).class_eval{ include M }
>  => #<Object:0x7fc61f1a1e58>
>
>  def o.x; X; end

This cannot work since X is not statically in scope.

>  o.x
>  => NameError: uninitialized constant X
>          from (irb):6:in `x'
>          from (irb):7
>
> The "(class << o; self; end).class_eval{ include M }" is effectively
> the same as "o.extend M" but I want to emphasize the use of #include.
>
> It of course works fine if I use an explicit class.
>
>  class O
>    include M
>    def x; X; end
>  end
>
>  O.new.x
>  => M::X

Yes, but you also changed something else: you defined the method
inside the class body.  So you did not only switch from class to
singleton class but you also changed the lookup.  It works if you
define the method in the class body in the same way as you did for
class O:

irb(main):001:0> module M
irb(main):002:1>   class X; end
irb(main):003:1> end
=> nil
irb(main):004:0> o = Object.new
=> #<Object:0x1016f240>
irb(main):005:0> (class << o; self; end).class_eval do
irb(main):006:1*   include M
irb(main):007:1>   def x; X; end
irb(main):008:1> end
=> nil
irb(main):009:0> o.x
=> M::X
irb(main):010:0> (class << o; self; end).class_eval do
irb(main):011:1*   def y; X; end
irb(main):012:1> end
=> nil
irb(main):013:0> o.y
=> M::X
irb(main):014:0>

Kind regards

robert

-- 
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