gistfile1.rb

class Bing
  def self.attr_with_defaults(hash={})
    hash.each do |name, value|
      attr_writer name
      define_method(name) do
        instance_variable_defined?("@#{name}") ? instance_variable_get("@#{name}") : value
      end
    end
  end
end
# => nil
class Bing
  attr_with_defaults :john => "cutie"
end
# => {:john=>"cutie"}
b = Bing.new
# => #<Bing:0x00000102825980 @john="carl">
b.john
# => "cutie"
b.john = "carl"
# => "carl"
b.john
# => "carl"