如何创建的toString扩展方法？ [英] How to create extension method for toString?

问题描述

我已经试过这种

public static class ListHelper
{
    public static string ToString<T>(this IList<String> list)
    {
        return string.Join(", ", list.ToArray());
    }

    public static string ToString<T>(this String[] array)
    {
        return string.Join(", ", array);
    }
}

但它不工作，都为的String []和列表。也许我需要一些特殊的注解？

but it does not work, both for string[] and List. Maybe I need some special annotations?

推荐答案

扩展方法只检查是否存在的没有适用的候选方法那场比赛。在通话的ToString方法的情况下会有的总是的是适用的候选方法，即对对象的ToString。的扩展方法的目的是要的延伸的的方法集可在一个类型，而不是<青霉>倍率的现有的方法;这就是为什么他们是所谓的扩展方法。如果要覆盖现有的方法，那么你就必须做出一个压倒一切的方法。

Extension methods are only checked if there are no applicable candidate methods that match. In the case of a call to ToString there will always be an applicable candidate method, namely, the ToString on object. The purpose of extension methods is to extend the set of methods available on a type, not to override existing methods; that's why they're called "extension methods". If you want to override an existing method then you'll have to make an overriding method.

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