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Can you show another example, then, of how one might implement the "magic" of Dwemthy's Array (http://poignantguide.net/dwemthy/) just using modules? I can never remember how to do this sort of thing, and if modules can make it conceptually simpler it would be most useful.

class Creature
  def self.metaclass; class << self; self; end; end

  def self.traits( *arr )
    return @traits if arr.empty?

    attr_accessor(*arr)

    arr.each do |a|
      metaclass.instance_eval do
        define_method( a ) do |val|
          @traits ||= {}
          @traits[a] = val
        end
      end
    end

    class_eval do
      define_method( :initialize ) do
        self.class.traits.each do |k,v|
          instance_variable_set("@#{k}", v)
        end
      end
    end
  end
end

class Rabbit < Creature
  traits :bombs
  bombs 3
end

Rabbit.new.bombs # => 3

class Creature
  def self.traits( *arr )
    return @traits if arr.empty?

    attr_accessor(*arr)

    mod = Module.new do
      arr.each do |a|
        define_method( a ) do |val|
          @traits ||= {}
          @traits[a] = val
        end
      end
    end

    extend mod
    
    define_method( :initialize ) do
      self.class.traits.each do |k,v|
        instance_variable_set("@#{k}", v)
      end
    end
  end
end

class Rabbit < Creature
  traits :bombs
  bombs 3
end

Rabbit.new.bombs # => 3