From: Dorren <dorrenchen@...>
Date: 2007-06-03T01:45:18+09:00
Subject: Re: so lost on singleton, metaclass and virtual class

google group totally screwed up the code, here it is again:
--------------------------------------------------------------

# http://whytheluckystiff.net/articles/seeingMetaclassesClearly.html
class Object
  # The hidden singleton lurks behind everyone
  def metaclass; class << self; self; end; end

  def show_meta
    puts "--------- #{to_s} ------------"
    puts "oid:           " +
         "#{object_id} #{self.class.name}"
    puts "class.oid:     #{self.class.object_id} " +
         "#{self.class.class.name}"
    puts "metaclass.oid: #{metaclass.object_id} " +
         "#{self.class.metaclass.class.name}"

    o = Object.new         # show methods
    meta = metaclass
    puts "object methods: " +
         "#{(public_methods - o.public_methods).sort.inspect}"
    puts " class methods: " +
     "#{(self.class.public_methods -
o.class.public_methods).sort.inspect}"
    puts "  meta methods: " +
     "#{(meta.public_methods - Class.public_methods).sort.inspect}"
    puts
  end
end

# ------- fixtures for our test --------------
class A
  def initialize(v);    @v = v;           end
  def to_s;             @v;               end

  def m1;               "method1 "        end
  def self.class_m0;    "class method0";  end
end

b = A.new("b")
c = A.new("c")
b.show_meta
c.show_meta