指定类本身的通用类的基类约束 | 指定类本身的通用类的基类约束

本文介绍了指定类本身的通用类的基类约束的处理方法，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

昨天，我在向朋友们解释C#的通用约束.在演示where T : CLASSNAME约束时，我鞭打了这样的内容:

Yesterday, I was explaining C#'s generic constraints to my friends. When demonstrating the where T : CLASSNAME constraint, I whipped up something like this:

public class UnusableClass<T> where T : UnusableClass<T>
{
    public static int method(T input){
        return 0;
    }
}

看到它可以编译真的很惊讶.然而，经过一番思考，从编译器的角度来看，我认为这是完全合法的-UnusableClass<T>与该约束中可以使用的任何其他类一样多.

And was really surprised to see it compile. After a bit of thinking, however, I figured it was perfectly legal from the point of view of the compiler - UnusableClass<T> is as much of a class as any other that can be used in this constraint.

但是，这留下了两个问题:如何使用此类?有可能

However, that leaves a couple of questions: how can this class ever be used? Is it possible to

实例化吗?
要继承吗?
调用其静态方法int method?

如果可以，怎么办?

如果这些中的任何一个是可能的，T的类型是什么?

If any of these is possible, what would the type of T be?

推荐答案

好吧.

public class Implementation : UnusableClass<Implementation>
{
}

完全有效，正因如此

var unusable = new UnusableClass<Implementation>();

和

UnusableClass<Implementation>.method(new Implementation());

有效.

因此，可以的，可以通过提供一个继承类型作为type参数来实例化，并且与对static方法的调用类似.例如，它对于树状结构很有用，您需要在该树状结构中通常指定节点具有的子代类型，而节点本身的类型相同.

So, yes, it can be instantiated by supplying an inheriting type as the type parameter, and similarly with the call to the static method. It's for instance useful for tree-like structures where you want to generically specify the type of children the node has, while it being the same type itself.

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