如何为ToString创建扩展方法？ [英] How to create an extension method for ToString?

问题描述

我已经尝试过：

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);
    }
}

但是对于<$ c都无效$ c> string [] 和 List< string> 。也许我需要一些特殊的注释？

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

推荐答案

仅在没有不适用候选方法的情况下才检查扩展方法 >匹配。在调用 ToString（）的情况下，总是将是适用的候选方法，即 ToString（ ）放在对象上。扩展方法的目的是扩展在一个类型上可用的方法集，而不是覆盖现有方法。这就是为什么它们被称为扩展方法的原因。如果要覆盖现有方法，则必须制作一个覆盖方法。

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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