record.rb

  class Record
    class MissingField < Error; end
    class << self
      def build(hash)
        new(*members.map{|m| hash[m.to_s] })
      end
    end
    def initialize(*values)
      self.class.members.zip(values).each do |member, value|
        raise MissingField, "Unable to initialize #{self.class}, missing field: '#{member}'." if value.nil?
        (class << self; self end).send(:define_method, member) do
          value
        end
      end
    end
  end

  class CreatureRecord < Record
    class << self
      def members
        %i[name perception]
      end
    end
  end