协方差此外，在3.5 / 2.0？ [英] Covariance Also in 3.5 / 2.0?

问题描述

奇怪的问题...

从伊夫例如实施协方差。

Ive implemented covariance from example .

我的目标FW为4.0。

My target FW is 4.0.

如何过。我想看看如果失败3.5 / 2 - >，但它不会。

How ever . I wanted to see if it fails on 3.5 /2 -> but it wont.

这是不能忽视的，因为协方差为FW4.0。

It cant be since covariance is from FW4.0.

更改为3.0，制作并看到后：（+在运行时不会失败）

After changing to 3.0 i Build and see : (+wont fail on runtime)

推荐答案

协方差框架3的支持，但是在编译器中没有实现。您正在使用的编译器4目标框架3。

Covariance was supported in framework 3, but not implemented in the compiler. You are using compiler 4 targeting framework 3.

这是提到在埃里克利珀博客后，我去看看我能找到它。

This is mentioned in an Eric Lippert blog post, I'll see if I can find it..

修改

要进一步明确，：公共语言运行库和C＃编译器（Csc.exe）是两个不同的东西。协变和逆变凡在2.0版中引入的CLR。他们没有被引入到C＃，直到第4版您正在使用的编译器4来版订做3 IL这就是为什么它的工作原理。

To further clarify,: The Common Language Runtime and the C# compiler (csc.exe) are two separate things. Covariance and Contravariance where introduced to the CLR at version 2.0. They were not introduced to C# until version 4. You are using Compiler 4 to build version 3 IL which is why it works.

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