对于预期操作不起作用通用约束

本文介绍了对于预期操作不起作用通用约束的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我有一些无法理解，为什么下面的代码片段并没有给我一个错误

I am having some trouble understanding why the following snippet does not give me an error

public void SomeMethod<T>(T arg) where T : MyInterface { MyInterface e = arg; }

不过，这一次，我希望由于工作的泛型类型约束

But this one, which I would expect to work due to the generic type constraint

private readonly IList<Action<MyInterface>> myActionList = new List<Action<MyInterface>>(); public IDisposable Subscribe<T>(Action<T> callback) where T: MyInterface { myActionList.Add(callback); // doesn't compile return null }

给出了这样的错误

Gives this error

cannot convert from 'System.Action<T>' to 'System.Action<MyInterface>'

我使用VS2012 SP1和.NET 4.5。

I am using VS2012 sp1 and .NET 4.5.

任何人都可以解释为什么限制不允许这种编译？

Can anyone explain why the constraint does not allow this to compile?

推荐答案

类和代表们不一样的东西。 System.Action＆LT; MyInterface的＆GT; 重$ P $类型的单个参数psents功能 MyInterface的，而 System.Action＆LT; T＆GT; 重presents的方法与类型 T：MyInterface的。该函数签名不兼容，它不相应和的 T 是 MyInterface的的衍生物，签名就只能是兼容如果 T 正是 MyInterface的。

Classes and delegates are not the same thing. System.Action<MyInterface> represents a function with a single parameter of type MyInterface whilst System.Action<T> represents a method with a parameter of type T : MyInterface. The function signatures are not compatible, it is not relevent that T is a derivative of MyInterface, the signature would only be compatible if T was exactly MyInterface.