My example showing dynamic top level instance variables with attrs for #ruby IRC

attributes.rb

class Attributes < Module
  def initialize(**attributes)
    self.class.class_eval do
      define_method :included do |klass|
        klass.class_eval do
          attributes.each do |key, value|
            instance_variable_set "@#{key}", value
            singleton_class.class_eval { attr_accessor key }
          end
        end
      end
    end
  end
end

module Universe
  include Attributes.new(meaning: 42, size: nil)
end

pp Universe.meaning
#>> 42

Universe.size = Float::INFINITY
pp Universe.size
#>> Infinity