C# 指定依赖于其他泛型类的泛型约束

我有以下几点：

// This part is fine
abstract class Attack {}

abstract class Unit<A> where A : Attack {}

class InstantAttack : Attack {}
class Infantry : Unit<InstantAttack> {}

// I'm lost here, on this part's syntax:
abstract class Controller<U> where U : Unit {}
// I want the above class to take any kind of Unit, but Unit is a generic class!

这肯定不管用。执行此操作的正确语法是什么？

如下所示：

abstract class Controller<U, A> where U : Unit<A> {}

interface IUnit { }
abstract class Unit<A> : IUnit where A : Attack { }
abstract class Controller<U> where U : IUnit { }

抽象类控制器，其中U:Unit{}

或者像这样：

abstract class Controller<U, A> where U : Unit<A> {}

interface IUnit { }
abstract class Unit<A> : IUnit where A : Attack { }
abstract class Controller<U> where U : IUnit { }

接口IUnit{}
抽象类单元：IUnit，其中A:Attack{}
抽象类控制器，其中U:IUnit{}