c# - 转换到一个奇怪的重复派生类

Question

我有一个使用奇怪重复模板模式的代码库，带有一个基类和一个派生类。
在接受基类参数的某个方法中，我想检查我收到的参数是否为派生类型，但我无法强制转换为它。
这是一个说明问题的示例:

class Base<T> where T : Base<T> {
}

class Derived<T> : Base<T>
    where T : Derived<T> { 
}

class DerivedBanana : Derived<DerivedBanana> { 
}

class Program {

    static void DoSomething<T>(T t) where T : Base<T> {
        // CS0311: The type 'T' cannot be used as type parameter 'T' in the generic type or method 'Derived<T>'.
        // There is no implicit reference conversion from 'T' to 'Derived<T>'.
        var d = t as Derived<T>;
    }

    static void Main(string[] args) {
        DoSomething(new DerivedBanana());
    }
}

有什么办法可以在我的 DoSomething 中登记吗？方法如果 T我得到的参数实际上是一个 Derived<T> ?
备注 :我正在重构我的代码以避免这种情况，但我仍然想知道如何进行这样的转换:)
注释 2 :建议的重复项没有回答我的问题:我想知道如何转换为派生类型，而不仅仅是检查变量是否为派生类型。

Answer 1

Is there a way I can check in my DoSomething method if the T parameterI'm getting is actually a Derived?

Derived<T>类可以用 Base<T> 约束获得更弱的类型安全形式

public class Base<T> where T : Base<T>
{
    public virtual Base<T> This(){
        return this as T;
    }
}

public class Derived<T> : Base<T>
    where T: Base<T>
{
    public override Derived<T> This()
    {
        return base.This() as Derived<T>;
    }
}

class DerivedBanana : Derived<DerivedBanana>
{
}

class BaseBanana : Base<BaseBanana>
{
}


class Program
{

    static void DoSomething<T>(T t) where T : Base<T>
    {
        
        T d = (T)(t.This() as Derived<T> ?? t.This() as Base<T>); 
        Console.WriteLine(d.GetType());
    }

    static void Main(string[] args)
    {   
        DoSomething(new BaseBanana());
        DoSomething(new DerivedBanana());
    }
}