如何限制泛型函数只接受某些类型的类 [英] How to restrict generic function to accept only some type of classes

问题描述

我正在尝试执行以下操作:

I'm trying to do the following:

public class A
{
}

public class B
{
}

在项目的某个地方我想要这个:

Somewhere along the project I want to have this:

public class C
{
    public T func<T>(T obj) [where T can be either of class A or class B]
    {
        obj.x = 100;

        return obj;
    }
}

我一直在尝试:

public T func<T>(T obj) where T: A, B

但这给了我

类型类约束'B'必须位于其他任何约束之前.

The type class constraint 'B' must come before any other constraint.

有人可以解释我如何使 func 仅接受A类或B类吗?

Can someone explain me how to make func accept only class A or class B?

推荐答案

正如问题中所描述的那样，此工作最好由超载分辨率处理:

Exactly as it's described in the question, this job is better handled by overload resolution:

public class C
{
    public A func(A obj)
    {
        obj.x = 100;   
        return obj;
    }

    public B func(B obj)
    {
        obj.x = 100;   
        return obj;
    }

}

但是我知道A和B可能是任意数量的类型的占位符，并且将它们全部考虑在内可能会很乏味.在这种情况下，您需要每个类都支持的通用接口:

But I understand that A and B may be placeholders for any number of types, and it could get tedious to account for them all. In that case, you'll need a common interface that's supported by each of your classes:

interface IBase
{
    int x;
}

public class C
{
    public IBase func(IBase obj)
    {
        obj.x = 100;   
        return obj;
    }
}

请注意，此时我们仍然不需要泛型.此外，您可能需要支持在通用界面下无法完全融合在一起的多种类型.在这种情况下，仍会构建接口，并在该接口中放置尽可能多的类型.如果需要，可以为更多类型创建另一个接口...依此类推...然后在接口和特定类型之间可以使用重载解析来处理事情.

Note that at this point we still have no need of generics. Additionally, you may need to support a number of types that won't all fit together under a common interface. In this case, still build the interface and put as many types with that interface as possible. If needed, build another interface for a few more types ... and so on... and then between interfaces and specific types you can handle things with overload resolution.

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