如何获取 IEnumerable 中元素的索引? [英] How to get the index of an element in an IEnumerable?

问题描述

我是这样写的:

public static class EnumerableExtensions
{
    public static int IndexOf<T>(this IEnumerable<T> obj, T value)
    {
        return obj
            .Select((a, i) => (a.Equals(value)) ? i : -1)
            .Max();
    }

    public static int IndexOf<T>(this IEnumerable<T> obj, T value
           , IEqualityComparer<T> comparer)
    {
        return obj
            .Select((a, i) => (comparer.Equals(a, value)) ? i : -1)
            .Max();
    }
}

但我不知道它是否已经存在，是吗?

But I don't know if it already exists, does it?

推荐答案

将内容作为 IEnumerable 的全部意义在于，您可以懒惰地迭代内容.因此，没有真正索引的概念.对于 IEnumerable，您正在做的事情确实没有多大意义.如果您需要支持按索引访问的内容，请将其放入实际列表或集合中.

The whole point of getting things out as IEnumerable is so you can lazily iterate over the contents. As such, there isn't really a concept of an index. What you are doing really doesn't make a lot of sense for an IEnumerable. If you need something that supports access by index, put it in an actual list or collection.

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