Ruby meta-programming

eigenclass.rb

module Extended
  refine Object do
    alias_method :eigenclass, :singleton_class

    # http://melborne.github.io/2012/07/12/object-repeat-take-care-of-sequence/
    def repeat(init = true) # assume &block is given
      x = self
      Enumerator.new do |y|
        y << x if init
        loop { y << (x = yield x) }
      end
    end
  end

  refine Class do
    alias_method :metaclass, :singleton_class
  end
end

using Extended

require 'pp'

# pp Class.singleton_class
pp Class.metaclass

puts

# pp Class.repeat(&:singleton_class).take(7)
pp *Class.repeat { |klass| klass.metaclass }.take(7)

puts

pp Class.repeat(&:itself).take(3)

rec_mod.rb

# cyclic chain
module Rec
  include self
rescue StandardError => e
  p e
end

Ruby's meta* class

stdout

#<Class:Class>

Class
#<Class:Class>
#<Class:#<Class:Class>>
#<Class:#<Class:#<Class:Class>>>
#<Class:#<Class:#<Class:#<Class:Class>>>>
#<Class:#<Class:#<Class:#<Class:#<Class:Class>>>>>
#<Class:#<Class:#<Class:#<Class:#<Class:#<Class:Class>>>>>>

[Class, Class, Class]

http://ideone.com/RIFcIH

https://bugs.ruby-lang.org/issues/6758

# generate enum by func
class Enumerator
  class << self
    def produce(obj, &block)
      new do |y|
        y << obj
        loop { y << (obj = yield obj) }
      end
    end
  end
end

init オプションは drop で十分