class A {     function __construct()     {         $a = func_get_args();         $i = func_num_args();         if (method_exists($this,$f='__construct'.$i)) {             call_user_func_array(array($this,$f),$a);         }     }         function __construct1($a1)     {         echo('__construct with 1 param called: '.$a1.PHP_EOL);     }         function __construct2($a1,$a2)     {         echo('__construct with 2 params called: '.$a1.','.$a2.PHP_EOL);     }         function __construct3($a1,$a2,$a3)     {         echo('__construct with 3 params called: '.$a1.','.$a2.','.$a3.PHP_EOL);     } } $o = new A('sheep'); $o = new A('sheep','cat'); $o = new A('sheep','cat','dog');

　　参考：http://php.net/manual/zh/language.oop5.decon.php