例如我有课程
trait Advert
case class Car(brand: String) extends Advert
case class House(price: Long) extends Advert
object AdvertCompanion[T <: Advert]
object Car extends AdvertComnation[Car]
object House extends AdvertComnation[House]
我不想在案例类的每个伴侣中写Json.writes [..]。我想在对象AdvertCompanion中编写它。但是我这样做，我得到错误No unapply function found