Scala:根据另一个参数的类型成员约束参数的类型

Question

我有两个特征,每个特征都有一个成员的类型参数.在第一个特征中,我有一个函数,它接受第二个特征的实例和第二个特征的类型成员的实例.此函数调用第二个特征中的函数,该函数期望其类型成员的实例.但是,我无法弄清楚如何正确地参数化调用,以便这实际上有效.这是一个失败的简化示例:

trait Garage {
  type CarType <: Car
  def Cars: Seq[CarType]

  def copy(Cars: Seq[CarType]): Garage

  def Refuel(car: CarType, fuel: CarType#FuelType): Garage = {
    val car_index = Cars.zipWithIndex.find(_._1 == car).get._2

    copy(Cars.updated(car_index, car.Refuel(fuel)))
  }
}

trait Car {
  type FuelType <: Fuel
  def Fuel: FuelType

  def copy(Fuel: FuelType): Car

  def Refuel(fuel: FuelType): Car = {
    copy(fuel)
  }
}

trait Fuel

此操作失败,并显示以下错误:

error: type mismatch;
 found   : fuel.type (with underlying type Garage.this.CarType#FuelType)
 required: car.FuelType
    copy(Cars.updated(car_index, car.Refuel(fuel)))
                                            ^

如何约束Garage.Refuel函数以使其接受a Car和Fuel该类型可接受的任何函数Car？

Answer 1

尝试:

def Refuel(car: CarType)(fuel: car.FuelType): Garage = {