PHP设计模式：用于解决特定软件问题的模式

interface VehicleInterface
{
    public function createVehicle();
}

class CarFactory implements VehicleInterface
{
    public function createVehicle()
    {
        return new Car();
    }
}

class BikeFactory implements VehicleInterface
{
    public function createVehicle()
    {
        return new Bike();
    }
}

// 使用工厂
$carFactory = new CarFactory();
$car = $carFactory->createVehicle();

$bikeFactory = new BikeFactory();
$bike = $bikeFactory->createVehicle();

class Cart implements SplSubject
{
    private $observers = [];
    private $items = [];

    public function attach(SplObserver $observer)
    {
        $this->observers[] = $observer;
    }

    public function detach(SplObserver $observer)
    {
        if (in_array($observer, $this->observers)) {
            unset($this->observers[array_search($observer, $this->observers)]);
        }
    }

    public function notify()
    {
        foreach ($this->observers as $observer) {
            $observer->update($this);
        }
    }

    public function addItem($item)
    {
        $this->items[] = $item;
        $this->notify();
    }

    public function removeItem($item)
    {
        $key = array_search($item, $this->items);
        if ($key !== false) {
            unset($this->items[$key]);
            $this->notify();
        }
    }
}

class OrderStatusObserver implements SplObserver
{
    public function update(SplSubject $subject)
    {
        if ($subject instanceof Cart) {
            echo "Order status has been updated.\n";
        }
    }
}

// 使用观察者模式
$cart = new Cart();
$orderStatusObserver = new OrderStatusObserver();
$cart->attach($orderStatusObserver);

// 模拟添加和删除商品
$cart->addItem('Item A');
$cart->removeItem('Item B');