from outside immutable class attributes

attributes.rb

module Attributes
  def has_attributes(*key_names)
    key_names.each do |key_name|
      define_method key_name do
        instance_variable_get("@attributes")[key_name]
      end
      define_method "#{key_name}=" do |value|
        instance_variable_get("@attributes")[key_name] = value
      end
    end
  end
end

class Foo
  extend Attributes
  has_attributes :one, :two
  def initialize(attributes)
    @attributes = {}.update(attributes)
  end
end