[英]Cannot return concrete implementation of constraint generic
I have some problem around generics and I don't see my mistake. 我在仿制药方面遇到了一些问题,我没有看到我的错误。
Given this code: 鉴于此代码:
public interface IMyInterface { }
public class MyImplementation : IMyInterface { }
public interface IMyFactory<T> where T : class, IMyInterface
{
T Create();
}
public class MyFactory<T> : IMyFactory<T> where T : class, IMyInterface
{
public T Create()
{
// Complex logic here to determine what i would like to give back
return new MyImplementation(); // <--- red squigglies - Cannot implicitly convert type 'ConsoleApp18.MyImplementation' to 'T'
}
}
If I use it like this return new MyImplementation() as T;
如果我像这样使用它
return new MyImplementation() as T;
it works. 有用。 No more errors are present.
不再存在错误。
If I use it like this return (T)new MyImplementation();
如果我像这样使用它
return (T)new MyImplementation();
i get a code suggestion to remove the unnecessary cast. 我得到一个代码建议删除不必要的演员。 (Yeah that's what I think too, why is it not possible to return the concrete implementation since it is compatible with T?) and also the first error (Cannot implicitly convert...) is still present.
(是的,这也是我的想法,为什么不能返回具体的实现,因为它与T兼容?)并且第一个错误(不能隐式转换...)仍然存在。
So why do I get this error and what is the correct implementation to return my concrete implementation? 那么为什么我会得到这个错误以及返回具体实现的正确实现是什么?
I have some problem around generics and I don't see my mistake.
我在仿制药方面遇到了一些问题,我没有看到我的错误。
Your mistake is to use generics. 你的错误是使用泛型。 Given the code you shown, you don't need them at all.
鉴于您显示的代码,您根本不需要它们。 The factory should return a
IMyInterface
instead of T
. 工厂应返回
IMyInterface
而不是T
public interface IMyFactory
{
IMyInterface Create();
}
public class MyFactory : IMyFactory
{
public IMyInterface Create()
{
// Complex logic here to determine what i would like to give back
return new MyImplementation();
}
}
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