循环中的 Lambda 变量捕获 - 这里发生了什么? [英] Lambda variable capture in loop - what happens here?

问题描述

我正在努力解决问题，这里发生了什么?编译器生成什么样的代码?

I am trying to get my head around, what happens here ? What sort of code does the compiler produce?

public static void vc()
{
    var listActions = new List<Action>();

    foreach (int i in Enumerable.Range(1, 10))
    {
        listActions.Add(() => Console.WriteLine(i));
    }

    foreach (Action action in listActions)
    {
        action();
    }
}

static void Main(string[] args)
{ 
  vc();
}

输出:1010..10

根据this，ActionHelper 的新实例将是为每次迭代创建.所以在那种情况下，我认为它应该打印 1..10.有人能给我一些关于编译器在这里做什么的伪代码吗?

According to this, a new instance of ActionHelper would be created for every iteration. So in that case, I would assume it should print 1..10. Can someone give me some pseudo code of what the compiler is doing here ?

谢谢.

推荐答案

在这一行

 listActions.Add(() => Console.WriteLine(i));

变量 i 被捕获，或者，如果您愿意，可以创建一个 指针 到该变量的内存位置.这意味着每个委托都有一个指向该内存位置的指针.在这个循环执行之后:

the variable i, is captured, or if you wish, created a pointer to the memory location of that variable. That means that every delegate got a pointer to that memory location. After this loop execution:

foreach (int i in Enumerable.Range(1, 10))
{
    listActions.Add(() => Console.WriteLine(i));
}

由于显而易见的原因i是10，所以Action(s)中存在的所有指针指向的内存内容变为10.

for obvious reasons i is 10, so the memory content that all pointers present in Action(s) are pointing, becomes 10.

换句话说，i 被捕获了.

In other words, i is captured.

顺便说一下，应该注意的是，根据 Eric Lippert 的说法，这种奇怪"的行为将在 C# 5.0 中解决.

By the way, should note, that according to Eric Lippert, this "strange" behaviour would be resolved in C# 5.0.

因此在 C# 5.0 中，您的程序将按预期打印:

So in the C# 5.0 your program would print as expected:

1,2,3,4,5...10

找不到埃里克·利珀特 (Eric Lippert) 关于主题的帖子，但这里有另一个:

Can not find Eric Lippert's post on subject, but here is another one:

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