List< T>投放算法和性能注意事项 [英] List<T> Casting algorithms and performance considerations

问题描述

我有以下代码

class Program
    {
        static void Main(string[] args)
        {
            List<A> aList = new List<A>();

            var aObj = new A();

            aObj.Go(aList.Cast<IB>());
        }
    }

    class A : IB
    {
        public void Go(IEnumerable<IB> interfaceList)
        {
            foreach (IB ibby in interfaceList)
            {
                Console.WriteLine("Here");
            }
        }
    }

    interface IB
    {
        void Go(IEnumerable<IB> interfaceList);
    }

}

我最初尝试传递一个列表，但是无效。
在 SO 的大量帮助下，我发现传递IEnumerable是将对象作为.ofType（IB）传递的唯一方法。

I originally tried passing a List but that doesn't work. After a lot of help from SO I found that passing IEnumerable is the only way to get the objects across as .ofType(IB).

对我来说不幸的是，在我的代码中，以下行将被执行数千次：

Unfortunately for me, in my code the following line will be executed thousands of times:

aList.Cast<IB>();

我想知道是否有人知道它是如何算法实现的（在IL中），它的时间顺序是什么。

I was wondering if anyone knew how it was implemented algorithmically (in IL) and what its time order is.

就是说，它比仅投射每个项目的foreach循环要快，还是它的作用到底是什么？

That is to say, is it faster than a foreach loop that just casts each item, or is that exactly what it does?

编辑主类需要维护实际对象的列表。但是只允许读者通过界面触摸它们。

EDIT The main class needs to maintain a list of the actual objects. But the reader is only allowed to touch them through the interface.

推荐答案

您应将 Go 更改为：

public void Go<T>(IEnumerable<T> interfaceList)
    where T : IB
{
    foreach (IB ibby in interfaceList)
    {
        Console.WriteLine("Here");
    }
}

那么您就可以了，不需要打电话发布。我怀疑Cast的源代码实现非常简单，尽管我认为它在3.5和3.5SP1之间发生了变化。但是，可能需要以常规迭代器块的方式设置新的状态机等。最好避免使用它。

Then you'll be fine with no need to call Cast. I suspect the source code implementation of Cast is pretty simple, although I believe it changed between 3.5 and 3.5SP1. However, it probably needs to set up a new state machine etc in the normal iterator block fashion. Better to avoid it if possible.

即使新方法是通用的，类型推断通常也应该为您解决，因此您无需指定 T 明确。

Even though the new method is generic, type inference should usually take care of it for you so you don't need to specify T explicitly.

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