泛型類型的繼承

Question

讓我們假設我們有以下classess：

abstract class Vehicle {/**/}

class Truck : Vehicle {/**/}
class Bus : Vehicle {/**/}
//etc...

abstract class VehicleWheel<TVehicle> where TVehicle : Vehicle {/**/}

class TruckWheel : VehicleWheel<Truck> {/**/}
class BusWheel : VehicleWheel<Bus> {/**/}

現在，我想創建泛型類“VehicleWheelCarrier”，它繼承自Vehicle，並且有一個參數，它是任何類型的輪：

abstract class VehicleWheelCarrier<TWheel> : Vehicle where TWheel:VehicleWheel

不幸的是，這不能編譯，因為VehicleWheel需要參數。

怎么解決？

Answer 1

您需要第二個通用參數來定義所需的類型：

public abstract class VehicleWheelCarrier<TWheel, U> : Vehicle 
                                                     where TWheel:VehicleWheel<U> 
                                                     where U : Vehicle { }

編輯：這將阻止您制作如下的荒謬結構：

class BusWheelCarrier : VehicleWheelCarrier<BusWheel, Truck>{ }

有錯誤：

從BusWheel到VehicleWheel<Truck>沒有隱式引用轉換。

但這會奏效：

class BusWheelCarrier : VehicleWheelCarrier<BusWheel, Bus>{ }

Answer 2

您可以像這樣為輪子添加非通用基礎：

abstract class Vehicle {/**/}

class Truck : Vehicle {/**/}
class Bus : Vehicle {/**/}
//etc...

abstract class VehicleWheelBase { internal VehicleWheelBase() { } /*Non-generic definitions of Wheel*/}
abstract class VehicleWheel<TVehicle> : VehicleWheelBase where TVehicle : Vehicle {/**/}

class TruckWheel : VehicleWheel<Truck> {/**/}
class BusWheel : VehicleWheel<Bus> {/**/}

abstract class VehicleWheelCarrier<TWheel> : Vehicle where TWheel : VehicleWheelBase