From: Intransition <transfire@...>
Date: 2010-06-07T04:41:58+09:00
Subject: Singleton classes and Namespce

Do singleton classes not get the same namespace treatment as normal
classes?

  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

  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