有没有办法确定 C# 4.0 中接口/委托的方差？
现在，我们在 C# 中的接口和委托上有了通用协变和逆变，我只是好奇如果给定一个 Type，您可以计算出其通用参数的协变/逆变。我开始尝试编写自己的实现，它将查看给定类型的所有方法，并查看返回类型和/或参数是否与泛型参数中的类型匹配。问题是，即使我有这个：
public interface IFoo<T>
{
void DoSomething(T item);
}
使用我的逻辑，它看起来应该是逆变的，但由于我们实际上没有指定：
public interface IFoo<in T>
{
void DoSomething(T item);
}
（in 参数）它实际上并不是逆变的。这引出了我的问题：有没有办法确定通用参数的方差？
So now that we have generic Covariance and Contravariance on interfaces and delegates in C#, I was just curious if given a Type, you can figure out the covariance/contravariance of its generic arguments. I started trying to write my own implementation, which would look through all of the methods on a given type and see if the return types and or arguments match the types in the generic arguments. The problem is that even if I have this:
public interface IFoo<T>
{
void DoSomething(T item);
}
using my logic, it LOOKS like it should be contravariant, but since we didn't actually specify:
public interface IFoo<in T>
{
void DoSomething(T item);
}
(the in parameter) it isn't actually contravariant. Which leads to my question: Is there a way to determine the variance of generic parameters?
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我不知道你为什么想要这个，但你可以从类型外部的反射来看待它。以下是有关使用反射查看类型的通用参数的信息：
http://msdn。 microsoft.com/en-us/library/b8ytshk6.aspx
具体来说，从调用 Type.GetGenericParameters 返回的类型上的属性 Type.GenericParameterAttributes 将显示泛型参数的 Co/Contravariance 属性。它是一个按位枚举，将显示以下信息的组合：
http ://msdn.microsoft.com/en-us/library/system.reflection.genericparameterattributes.aspx
真的很有趣...感谢您提出这个问题并让我查找它。
I don't know why you would want this, BUT you can look at it with reflection from outside of the type. Here's information on looking at Generic Parameters for a type using reflection:
http://msdn.microsoft.com/en-us/library/b8ytshk6.aspx
Specifically, the property Type.GenericParameterAttributes on the type you get back from a call to Type.GetGenericParameters will reveal the Co/Contravariance properties of the generic argument... it's a bitwise enum that will reveal the combination of this information:
http://msdn.microsoft.com/en-us/library/system.reflection.genericparameterattributes.aspx
Really interesting... thanks for asking this and making me look it up.