http://www.rubyquiz.com/quiz67.html

rubyquiz-67.rb

class Object
  
  def attribute(attribute, &block)
    attribute, default_value = attribute.to_a.first if attribute.is_a?(Hash)    

    define_method(:"#{attribute}") do
      if instance_variables.include?("@#{attribute}")
        instance_variable_get("@#{attribute}")
      elsif block_given?
        instance_eval(&block)
      else
        default_value
      end
    end

    define_method(:"#{attribute}?") { !!send(attribute.to_sym) }
    define_method(:"#{attribute}=") { |args| instance_variable_set("@#{attribute}", args) }
  end

end