IEnumerable< T> .Reverse是如何工作的？

问题描述：

我检查了反射器中的代码，但是我还没有找到它如何枚举通过一个集合向后？

I am checking out the code in the reflector, but I haven't yet found out how it can enumerate through a collection backwards?

因为没有计数信息和枚举总是从集合的开始开始，是吗？

Since there is no count information, and enumeration always starts from the "start" of the collection, right?

这是.NET框架中的一个缺点吗？成本是否高于常规枚举？

Is it a drawback in the .NET framework? Is the cost higher than regular enumeration?

答

简而言之，它缓冲一切，然后向后走。不太有效，但是从那个角度来看，OrderBy也不是。

In short, it buffers everything and then walks through it backwards. Not efficient, but then, neither is OrderBy from that perspective.

在LINQ-to-Objects中，有缓冲操作（Reverse，OrderBy，GroupBy等）缓冲操作（其中，Take，Skip等）。

In LINQ-to-Objects, there are buffering operations (Reverse, OrderBy, GroupBy, etc) and non-buffering operations (Where, Take, Skip, etc).

作为非缓冲的示例使用 IList< T> 执行

public static IEnumerable<T> Reverse<T>(this IList<T> list) {
    for (int i = list.Count - 1; i >= 0; i--) {
        yield return list[i];
    }
}

请注意，这仍然是一个小错误你在迭代它时改变列表...所以不要这样做;-p

Note that this is still a little susceptible to bugs if you mutate the list while iterating it... so don't do that ;-p