C＃：是与继承泛型类型运营商 [英] C#: Is operator for Generic Types with inheritance

问题描述

我与一个问题是运营商比较泛型类型

I have a problem with the is operator comparing generic types.

 public interface ISomeInterface<T> where T : SomeBaseClass{
 }

 public class SomeClass : SomeBaseClass{
 }

现在我们要检查与运营商是类型。我们有一个类实现接口ISomeInterface的一个实例。

Now we want to check the type with is operator. We have an instance of a class implementing interface ISomeInterface.

不幸的是，我们正面临着以下问题：

Unfortunatly we are facing following problem:

 // someObject is an Instance of a class implementing interface ISomeInterface<SomeClass>
 bool isSomeBaseClass = someObject is ISomeInterface<SomeBaseClass>; // false
 bool isSomeClass = someObject is ISomeInterface<SomeClass>; // true

时可以检查变量泛型类型？

Is it possible to check a variable generic type?

在此先感谢，
托比

Thanks in advance, Tobi

推荐答案

这就是所谓的通用协方差和支持C＃4.0。你可以标记与退出关键字通用 T 参数：

This is called generic covariance and is supported in C# 4.0. You could mark the generic T parameter with the out keyword:

public interface ISomeInterface<out T> where T : SomeBaseClass

这有一个限制，但。在 T 参数只能出现在接口中的方法返回类型。

This has a limitation though. The T parameter can only appear as return type of the methods in the interface.

埃里克利珀有一个<一个HREF =htt​​p://blogs.msdn.com/b/ericlippert/archive/tags/covariance+and+contravariance/default.aspx相对=nofollow>系列博客文章对这个问题的，我请您阅读。

Eric Lippert has a series of blog posts on this subject that I invite you to read.

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