コンストラクタでの初期化の一部を肩代わりしてくれるdefinit.rb

definit.rb

class Class

  def definit *params, &initialize
    define_method :initialize do |*args, &blk|
      until params.empty?
        instance_variable_set :"@#{params.shift.to_sym}", args.shift
      end
      initialize && instance_exec(*args, &initialize)
    end
  end

end

class Person

  attr_reader :name, :age, :sex, :type

  definit :name, :age, :sex do |type|
    @type = type || !@sex
  end

  def to_s
    "#@name #@age #@sex #@type"
  end

end

Mana = Person.new 'mana', 18, true
puts Mana