eigenclass_generator.rb

require 'fiber'

module Eigenclass
  def eigenclass
    class << self; self end 
  end 
  module_function :eigenclass
  public :eigenclass
end

class Object
  include Eigenclass
end

class EigenclassesGenerator
  def initialize(obj)
    @eigenclasses = [obj.eigenclass]

    @fiber = Fiber.new do
      loop do
        Fiber.yield @eigenclasses.last
        @eigenclasses[@eigenclasses.length] = @eigenclasses.last.eigenclass
      end 
    end 
  end 

  def [](index)
    (index - @eigenclasses.length + 2).times { @fiber.resume } if index >= @eigenclasses.length
    @eigenclasses[index]
  end 
end

# examples
eg = EigenclassesGenerator.new(String)

p eg[3]
p eg[5]
p eg[1]