C＃泛型和多态性：一个矛盾？ [英] C# Generics and polymorphism: an oxymoron?

问题描述

我只是想确认我所理解的关于泛型在C＃。这已经出现在一对夫妇的代码库，我在一个通用的基类，用于创建类型安全的衍生的实例工作。一个非常简单的例子，我在说一下，

I just want to confirm what I've understood about Generics in C#. This has come up in a couple code bases I've worked in where a generic base class is used to create type-safe derived instances. A very simple example of what I'm talking about,

public class SomeClass<T>
{
    public virtual void SomeMethod(){ }
}

public class DeriveFrom :SomeClass<string>
{
    public override void SomeMethod()
    {
        base.SomeMethod();
    }
}

，问题出现了，当我再要使用派生在一个多态的方式实例。

The problem comes up when I then want to use derived instances in a polymorphic way.

public class ClientCode
{
    public void DoSomethingClienty()
    {
        Factory factory = new Factory();
        //Doesn't compile because SomeClass needs a type parameter!
        SomeClass someInstance = factory.Create();

        someInstance.SomeMethod();
    }
}

看来，一旦你介绍一个通用成一个继承层次结构或接口，可以不再使用家庭类多态的方式也许除了内部本身。是真的吗？

It seems that once you introduce a Generic into an inheritance hierarchy or interface, you can no longer use that family of classes in a polymorphic way except perhaps internal to itself. Is that true?

推荐答案

据我所看到的，耗时的代码不需要泛型类的细节（也就是说，它不取决于什么 T 是）。那么，你为什么不引入接口 SomeClass的< T> 将实施，并使用这个接口的实例

As far as I can see, consuming code doesn't need specifics of generic class (i.e., it doesn't depends on what T is). So, why don't you introduce interface that SomeClass<T> will implement, and use instance of this interface.

例如：

public interface ISome
{
    void SomeMethod();
}

public class SomeClass<T>: ISome
{
    public virtual void SomeMethod(){ }
}

public void DoSomethingClienty()
{
    Factory factory = new Factory();
    ISome someInstance = factory.Create();

    someInstance.SomeMethod();
}

现在，子类 SomeClass的< T> 可以在不同的 T的运作方式不同 S，但消费的代码不会改变。

Now, subclasses of SomeClass<T> can operate differently on different Ts, but consuming code won't change.

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