default_constructor.rb

module DefaultConstructor
  def self.included(base)
    base.extend(ClassMethods)
  end

  module ClassMethods
    def constructor(*attributes)
      attr_reader *attributes

      define_method :initialize do |*attrs|
        attributes.zip(attrs).each do |attr, value|
          instance_variable_set("@#{attr}", value)
        end
      end
    end
  end
end

class Hoge
  include DefaultConstructor
  constructor :foo, :bar, :baz
end

hoge = Hoge.new(1, 2, 3)
p hoge.foo  # => 1
p hoge.bar  # => 2
p hoge.baz  # => 3

あとアリティのチェックも必要