gistfile1.rb

class Module
  def private(*args)
    if args.empty?
      @acl = :private
    else
      args.each do |meth|
        alias_method :"__#{meth}", meth
        undef_method meth
      end
    end
  end
  
  alias_method :orig_public, :public
  def public(*args)
    if args.empty?
      @acl = :public
    end
    orig_public
  end
  
  alias_method :orig_method_added, :method_added if self.instance_methods.include?(:method_added)
  def method_added(meth)
    return if meth.to_s =~ /^__/
    orig_method_added(meth) if self.respond_to?(:orig_method_added)
    if @acl && @acl == :private
      alias_method :"__#{meth}", meth
      public :"__#{meth}"
      undef_method meth
    end
  end
end

class N
  def zoo
    :zoo
  end
  
  def poo
    :poo
  end
  private :poo
  
  public
    def choo
      :choo
    end
  
  private
    def woo
      :woo
    end
  
  public
    def moo
      :moo
    end
end

n = N.new
n.poo
n.__poo
n.woo
n.__woo
n.zoo
n.choo
n.moo