blocks|key|1434306|text|我能找到的唯一解决方案是先制作一个本地副本：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1434307|for+(int+i+=+0;+i+<+10;+%2B%2Bi)
{
++++int+copy+=+i;
++++actions.Add(()+=>+Console.WriteLine(copy));
}|code-block|syntax|javascript|1434308|但是我很难理解为什么在for循环中放置一个副本与使用lambda捕获i有什么不同。|offset|length|style|CODE|1434309|entityMap^0|0|0|Y|1|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

The only solution I've been able to find is to make a local copy first:

<pre><code>for (int i = 0; i &lt; 10; ++i)
{
 int copy = i;
 actions.Add(() =&gt; Console.WriteLine(copy));
}
</code></pre>

But I'm having trouble understanding why putting a copy inside the for-loop is any different than having the lambda capture <code>i</code>.

blocks|key|1434352|text|唯一的解决方案是创建一个本地副本，并在lambda中引用它。当在闭包中访问C#+(和VB.Net)中的所有变量时，它们将具有引用语义与复制/值语义。在这两种语言中都无法更改此行为。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1434353|注意:它实际上不会作为引用进行编译。编译器将变量提升到闭包类中，并将对"i“的访问重定向到给定闭包类中的字段"i”。不过，通常更容易将其视为引用语义。|1434354|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

The only solution is to make a local copy and reference that within the lambda. All variables in C# (and VB.Net) when accessed in a closure will have reference semantics vs. copy/value semantics. There is no way to change this behavior in either language. 

Note: It doesn't actually compile as a reference. The compiler hoists the variable into a closure class and redirects accesses of "i" into a field "i" inside the given closure class. It's often easier to think of it as reference semantics though.

blocks|key|1649128|text|记住，lambda表达式实际上只是匿名方法的语法糖。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1649129|也就是说，您真正要找的是匿名方法如何在父作用域中使用局部变量。|1649130|这里有一个描述这一点的链接。http://www.codeproject.com/KB/cs/InsideAnonymousMethods.aspx#4|offset|length|1649131|entityMap|0|LINK|mutability|MUTABLE|url|http://www.codeproject.com/KB/cs/InsideAnonymousMethods.aspx#4^0|0|0|E|1Q|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@$F|S|G|T|1|U]]|A|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

Remember that lambda expressions are really only syntactic sugar for anonymous methods.

That being said, what you are really looking for is how anonymous methods use local variables in a parent scope. 

Here's a link describing this. <a href="http://www.codeproject.com/KB/cs/InsideAnonymousMethods.aspx#4" rel="nofollow noreferrer">http://www.codeproject.com/KB/cs/InsideAnonymousMethods.aspx#4</a>

blocks|key|1434450|text|编译器所做的是将您的lambda和lambda捕获的任何变量拉入编译器生成的嵌套类中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1434451|编译后，您的示例看起来很像这样：|1434452|class+Program
{
++++++++delegate+void+Action();
++++++++static+void+Main(string[]+args)
++++++++{
++++++++++++++++List<Action>+actions+=+new+List<Action>();

++++++++++++++++DisplayClass1+displayClass1+=+new+DisplayClass1();
++++++++++++++++for+(displayClass1.i+=+0;+displayClass1.i+<+10;+%2B%2BdisplayClass1.i+)
++++++++++++++++++++++++actions.Add(new+Action(displayClass1.Lambda));

++++++++++++++++foreach+(Action+a+in+actions)
++++++++++++++++++++++++a();
++++++++}

++++++++class+DisplayClass1
++++++++{
++++++++++++++++int+i;
++++++++++++++++void+Lambda()
++++++++++++++++{
++++++++++++++++++++++++Console.WriteLine(i);
++++++++++++++++}
++++++++}
}|code-block|syntax|javascript|1434453|通过在for循环中创建一个副本，编译器在每次迭代中生成新对象，如下所示：|1434454|for+(int+i+=+0;+i+<+10;+%2B%2Bi)
{
++++DisplayClass1+displayClass1+=+new+DisplayClass1();
++++displayClass1.i+=+i;
++++actions.Add(new+Action(displayClass1.Lambda));
}|1434455|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

What the compiler is doing is pulling your lambda and any variables captured by the lambda into a compiler generated nested class.

After compilation your example looks a lot like this:

<pre><code>class Program
{
 delegate void Action();
 static void Main(string[] args)
 {
 List&lt;Action&gt; actions = new List&lt;Action&gt;();

 DisplayClass1 displayClass1 = new DisplayClass1();
 for (displayClass1.i = 0; displayClass1.i &lt; 10; ++displayClass1.i )
 actions.Add(new Action(displayClass1.Lambda));

 foreach (Action a in actions)
 a();
 }

 class DisplayClass1
 {
 int i;
 void Lambda()
 {
 Console.WriteLine(i);
 }
 }
}
</code></pre>

By making a copy within the for loop, the compiler generates new objects in each iteration, like so:

<pre><code>for (int i = 0; i &lt; 10; ++i)
{
 DisplayClass1 displayClass1 = new DisplayClass1();
 displayClass1.i = i;
 actions.Add(new Action(displayClass1.Lambda));
}
</code></pre>

I've been learning C#, and I'm trying to understand lambdas. In this sample below, it prints out 10 ten times.

<pre><code>class Program
{
 delegate void Action();
 static void Main(string[] args)
 {
 List&lt;Action&gt; actions = new List&lt;Action&gt;();

 for (int i = 0; i &lt; 10; ++i )
 actions.Add(()=&gt;Console.WriteLine(i));

 foreach (Action a in actions)
 a();
 }
}
</code></pre>

Obviously, the generated class behind the lambda is storing a reference or pointer to the <code>int i</code> variable, and is assigning a new value to the same reference every time the loop iterates. Is there a way to force the lamda to grab a copy instead, like the C++0x syntax

<pre><code>[&amp;](){ ... } // Capture by reference
</code></pre>

vs.

<pre><code>[=](){ ... } // Capture copies
</code></pre>

How to tell a lambda function to capture a copy instead of a reference in C#?

编译器

我一直在学习C#，并试图理解lambdas。在下面的示例中，它打印了10次。class Program{ delegate void Action(); static void Main(string[] args) { List<Action> actions = new List<A...

问如何告诉lambda函数捕获一个副本，而不是C#中的引用？
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