# File lib/net/dns/rr/classes.rb, line 31
        def initialize(cls)
          case cls
            when String
              initialize_from_str(cls)
            when Fixnum
              initialize_from_num(cls)
            when nil
              initialize_from_num(@@default)
          end

          if @str.nil? || @num.nil?
            raise ArgumentError, "Unable to create a `Classes' from `#{cls}'"
          end
        end