PHP-类中的闭包，获取私有属性

我正试图使用闭包从另一个类获取私有属性，如下所述：

http://ocramius.github.io/blog/accessing-private-php-class-members-without-reflection/

所以，我正试图获得$wheelCount的财产。

但我一直在接受

Fatal error: Cannot access private property Car::$wheelCount

所以我的汽车等级是：

class Car
{
    private $wheelCount = 4;    
    public function __construct($wheely)
    {
             echo $wheely->getWheels($this);
    }
}

然后

   class getThoseWheels
    {
        public function getWheels($that)
        {
            $wheels = Closure::bind($this->getPrivate($that), null, $that);
            var_dump($wheels);

        }
        public function getPrivate($that)
        {
             return $that->wheelCount;
        }
    }

运行的：

$wheely = new getThoseWheels();
new Car($wheely);