在PHP5中的_destruct中自动取消设置所有类变量

class MyClass {
    public $variable1;
    public $variable2;

    public function __construct($var1, $var2) {
        $this->variable1 = $var1;
        $this->variable2 = $var2;
    }

    public function __destruct() {
        unset($this->variable1);
        unset($this->variable2);
    }
}

$obj = new MyClass("value1", "value2");
echo $obj->variable1 . " - " . $obj->variable2; // 输出 "value1 - value2"

unset($obj);
// 此时，$obj 不再被引用，__destruct() 方法将被自动调用