class abc{
            function   __construct()    {
              $num   =func_num_args();           switch ($num)        {               case 0:                   echo "none ";                 break;               case 1:                echo "one ";                 break;               case 2:                     echo "two ";                 break;           }       } }   new   abc()   ; new   abc(1)   ; new   abc(1,2);

函数的解析我就不写了，太简单了