({$ShopProduct->price})，这是什么意思？

具体代码：
class ShopProductWriter
{
　public function write($shopProduct)
　{
　　$str = "{$shopProduct->title}: " . $shopProduct->getProducer() . "({$ShopProduct->price})\n";
　　print($str);
　}
}
正在看《深入PHP，面向对象、模式与实践》，搞不懂书上这段代码为啥非要带括号({$ShopProduct->price})，求解答，谢谢。