仿制药的问题C＃继承 [英] C# inheritance in generics question

问题描述

我有两个接口：

public interface A { 
 void aMethod(); 
}


public interface B : A {
 void bMethod();
} 

后来我基本上使用这样的字典：

Later I'm basically using a dictionary like this:

Dictionary<int, A> dict = new Dictionary<int, B>();

C＃是说我不能从右边转化为左边，即使我投它。有没有办法使用泛型在C＃，使这个可以工作的方法吗？如果我让他们抽象类这似乎是确定，但我需要这些作为接口。

C# is saying I can't convert from the right to the left, even if I cast it. Is there a way to use generics in C# so that this can work? If I make them abstract classes it seems to be ok but I need these as interfaces.

推荐答案

您正在寻找的是特征什么是被称为仿制药方差（协方差和逆变）。有这个首发的.NET Framework 4，这里有一个有趣的帖子有限的支持：的通用协方差和孔特拉方差是如何实现在C＃4.0

The feature you are looking for is what's referred to as generics variance (covariance and contravariance). There is limited support for this starting in .net framework 4. Here's an interesting post: How is Generic Covariance & Contra-variance Implemented in C# 4.0?

和这里的的MSDN条目泛型。

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