archive.rb

module Archives
  module Callbacks
    def self.included(base)
      base.send :include, Archives::Callbacks::InstanceMethods
      base.before_create :do_something_awesome
    end

    module InstanceMethods
      private

      def do_something_awesome
        true
      end
    end
  end

  module Validations
    def self.included(base)
      base.send :include, Archives::Validations::InstanceMethods
      base.validate :something_is_correct
    end

    module InstanceMethods
      private

      def something_is_correct
        unless something.correct?
          errors.add(:something, "is SO not right")
        end
      end
    end
  end
end

class Archive < ActiveRecord::Base
  include Archives::Callbacks
  include Archives::Validations
end