C# - 如何为多级继承层次结构指定泛型类型约束？

Question

我有以下类层次结构

public class EntityBase<T> where T : EntityBase<T>
{
    //nothing interesting here
}

public class Benefit : EntityBase<Benefit>
{
    //again, nothing interesting here
}

public class SeasonTicketLoan : Benefit
{
    //nothing interesting here
}

现在我得到了如下界面

public interface IQuery<T> where T : EntityBase<T>
{
}

当我尝试构建以下类时出现编译错误

public class EmployeesQuery : IQuery<SeasonTicketLoan>
{
}

我收到一条错误消息，提示 SeasonTicketLoan 类不满足约束条件。

Answer 1

Benefit 类也应该有一个通用类型——因此所有父类都将"ultimate"/sealed 类型作为它们的通用类型。只有“最终”/密封类型没有通用参数。
结果是，在所有父类中一直到根父类，泛型参数包含“最终”/密封类的类型，并且不会出现错误。

public class EntityBase<T> where T : EntityBase<T>
{
    //nothing interesting here
}

public class Benefit<T> : EntityBase<T> where T : Benefit<T>
{
    //again, nothing interesting here
}

public sealed class SeasonTicketLoan : Benefit<SeasonTicketLoan>
{
    //nothing interesting here
}