blocks|key|3092340|text|在幕后，匿名方法是通过提升捕获的变量(这就是您的问题主体)并将它们存储为编译器生成的类的字段来实现的。无法将ref或out参数存储为字段。Eric+Lippert在a+blog+entry上讨论了这一点。请注意，捕获的变量和lambda参数之间存在差异。你可以像下面这样“形参”，因为它们不是被捕获的变量：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|3092341|delegate+void+TestDelegate+(out+int+x);
static+void+Main(string[]+args)
{
++++TestDelegate+testDel+=+(out+int+x)+=>+{+x+=+10;+};
++++int+p;
++++testDel(out+p);
++++Console.WriteLine(p);
}|code-block|syntax|javascript|3092342|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/de-de/archive/blogs/ericlippert/the-stack-is-an-implementation-detail-part-two^0|D|5|1I|3|1M|3|2A|C|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|D]|$9|Y|A|Z|B|D]]|E|@$9|10|A|11|1|12]]|F|$]]|$1|G|3|H|5|I|7|13|8|@]|E|@]|F|$J|K]]|$1|L|3|-4|5|6|7|14|8|@]|E|@]|F|$]]]|M|$N|$5|O|P|Q|F|$R|S]]]]

Under the hood, the anonymous method is implemented by hoisting captured variables (which is what your question body is all about) and storing them as fields of a compiler generated class. There is no way to store a <code>ref</code> or <code>out</code> parameter as a field. Eric Lippert discussed it in <a href="https://docs.microsoft.com/de-de/archive/blogs/ericlippert/the-stack-is-an-implementation-detail-part-two" rel="noreferrer">a blog entry</a>. Note that there is a difference between captured variables and lambda parameters. You can have "formal parameters" like the following as they are not captured variables:

<pre><code>delegate void TestDelegate (out int x);
static void Main(string[] args)
{
 TestDelegate testDel = (out int x) =&gt; { x = 10; };
 int p;
 testDel(out p);
 Console.WriteLine(p);
}
</code></pre>

blocks|key|3092397|text|Lambda看起来像是改变了它们捕获的变量的生命周期。例如，下面的lambda表达式会导致参数p1比当前方法框架存在的时间更长，因为它的值可以在方法框架不再位于堆栈中之后访问|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3092398|Func<int>+Example(int+p1)+{
++return+()+=>+p1;
}|code-block|syntax|javascript|3092399|捕获变量的另一个属性是，对变量的更改也可以在lambda表达式之外看到。例如，下面的打印42|3092400|void+Example2(int+p1)+{
++Action+del+=+()+=>+{+p1+=+42;+}
++del();
++Console.WriteLine(p1);
}|3092401|这两个属性以以下方式生成一组与ref参数冲突的特定效果|3092402|3092403|引用参数可以具有固定的生存期。考虑将局部变量作为ref参数传递给函数。lambda中的|unordered-list-item|3092404|副作用需要在ref参数本身上可见。无论是在方法中还是在调用方中。|3092405|3092406|这些属性有些不兼容，也是lambda表达式中不允许使用这些属性的原因之一。|3092407|entityMap^0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Z|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|11|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|12|8|@]|9|@]|A|$]]|$1|N|3|O|5|P|7|13|8|@]|9|@]|A|$]]|$1|Q|3|R|5|P|7|14|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|15|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|16|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|W|$]]

Lambdas have the appearance of changing the lifetime of variables that they capture. For instance the following lambda expression causes the parameter p1 to live longer than the current method frame as its value can be accessed after the method frame is no longer on the stack

<pre><code>Func&lt;int&gt; Example(int p1) {
 return () =&gt; p1;
}
</code></pre>

Another property of captured variables is that changes to the variable are also visible outside the lambda expression. For example the following prints 42

<pre><code>void Example2(int p1) {
 Action del = () =&gt; { p1 = 42; }
 del();
 Console.WriteLine(p1);
}
</code></pre>

These two properties produce a certain set of effects which fly in the face of a ref parameter in the following ways

<ul>
<li>ref parameters may have a fixed lifetime. Consider passing a local variable as a ref parameter to a function. </li>
<li>Side effects in the lambda would need to be visible on the ref parameter itself. Both within the method and in the caller. </li>
</ul>

These are somewhat incompatible properties and are one of the reasons they are disallowed in lambda expressions.

blocks|key|334919|text|由于这是谷歌上"C#+lambda+ref“的最高搜索结果之一，我觉得我需要在上面的答案上进行扩展。较早的(C#+2.0)匿名委托语法有效，它支持更复杂的签名(以及闭包)。Lambda和匿名委托至少在编译器后端共享了可感知的实现(如果它们不完全相同)-最重要的是，它们支持闭包。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|334920|当我进行搜索时，我想要做的是演示语法：|334921|public+static+ScanOperation<TToken>+CreateScanOperation(
++++PrattTokenDefinition<TNode,+TToken,+TParser,+TSelf>+tokenDefinition)
{
++++var+oldScanOperation+=+tokenDefinition.ScanOperation;+//+Closures+still+work.
++++return+delegate(string+text,+ref+int+position,+ref+PositionInformation+currentPosition)
++++++++{
++++++++++++var+token+=+oldScanOperation(text,+ref+position,+ref+currentPosition);
++++++++++++if+(token+==+null)
++++++++++++++++return+null;
++++++++++++if+(tokenDefinition.LeftDenotation+!=+null)
++++++++++++++++token._led+=+tokenDefinition.LeftDenotation(token);
++++++++++++if+(tokenDefinition.NullDenotation+!=+null)
++++++++++++++++token._nud+=+tokenDefinition.NullDenotation(token);
++++++++++++token.Identifier+=+tokenDefinition.Identifier;
++++++++++++token.LeftBindingPower+=+tokenDefinition.LeftBindingPower;
++++++++++++token.OnInitialize();
++++++++++++return+token;
++++++++};
}|code-block|syntax|javascript|334922|请记住，Lambdas在程序上和数学上更安全(因为前面提到的ref值提升)：您可能会打开一个蠕虫罐头。在使用此语法时，请仔细考虑。|334923|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

As this is one of the top results for "C# lambda ref" on Google; I feel I need to expand on the above answers. The older (C# 2.0) anonymous delegate syntax works and it does support more complex signatures (as well closures). Lambda's and anonymous delegates at the very least have shared perceived implementation in the compiler backend (if they are not identical) - and most importantly, they support closures.

What I was trying to do when I did the search, to demonstrate the syntax:

<pre><code>public static ScanOperation&lt;TToken&gt; CreateScanOperation(
 PrattTokenDefinition&lt;TNode, TToken, TParser, TSelf&gt; tokenDefinition)
{
 var oldScanOperation = tokenDefinition.ScanOperation; // Closures still work.
 return delegate(string text, ref int position, ref PositionInformation currentPosition)
 {
 var token = oldScanOperation(text, ref position, ref currentPosition);
 if (token == null)
 return null;
 if (tokenDefinition.LeftDenotation != null)
 token._led = tokenDefinition.LeftDenotation(token);
 if (tokenDefinition.NullDenotation != null)
 token._nud = tokenDefinition.NullDenotation(token);
 token.Identifier = tokenDefinition.Identifier;
 token.LeftBindingPower = tokenDefinition.LeftBindingPower;
 token.OnInitialize();
 return token;
 };
}
</code></pre>

Just keep in mind that Lambdas are procedurally and mathematically safer (because of the ref value promotion mentioned earlier): you might open a can of worms. Think carefully when using this syntax.

blocks|key|3305266|text|您可以，但必须显式定义所有类型，以便|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3305267|(a,+b,+c,+ref+d)+=>+{...}|code-block|syntax|javascript|3305268|是无效的，但是|3305269|(int+a,+int+b,+int+c,+ref+int+d)+=>+{...}|3305270|是有效的|3305271|entityMap^0|0|0|0|0|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]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

You can but you must explicitly define all the types so

<pre><code>(a, b, c, ref d) =&gt; {...}
</code></pre>

Is invalid, however

<pre><code>(int a, int b, int c, ref int d) =&gt; {...}
</code></pre>

Is valid

blocks|key|3092581|text|还有这个呢？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3092582|private+void+Foo()
{
++++int+value;
++++Bar(out+value);
}

private+void+Bar(out+int+value)
{
++++value+=+3;
++++int[]+array+=+{+1,+2,+3,+4,+5+};
++++var+val+=+value;+
++++int+newValue+=+array.Where(a+=>+a+==+val).First();
}|code-block|syntax|javascript|3092583|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

And maybe this?

<pre><code>private void Foo()
{
 int value;
 Bar(out value);
}

private void Bar(out int value)
{
 value = 3;
 int[] array = { 1, 2, 3, 4, 5 };
 var val = value; 
 int newValue = array.Where(a =&gt; a == val).First();
}
</code></pre>

Why can't you use a ref or out parameter in a lambda expression?

I came across the error today and found a workaround but I was still curious why this is a compile-time error.

<blockquote>
 <a href="https://docs.microsoft.com/en-us/dotnet/csharp/misc/cs1628" rel="noreferrer">CS1628</a>: Cannot use in ref or out parameter 'parameter' inside an anonymous method, lambda expression, or query expression
</blockquote>

Here's a simple example:

<pre><code>private void Foo()
{
 int value;
 Bar(out value);
}

private void Bar(out int value)
{
 value = 3;
 int[] array = { 1, 2, 3, 4, 5 };
 int newValue = array.Where(a =&gt; a == value).First();
}
</code></pre>

Cannot use ref or out parameter in lambda expressions

为什么不能在lambda表达式中使用ref或out参数呢？我今天遇到了这个错误，并找到了一种解决方法，但我仍然很好奇为什么这是一个编译时错误。参数:不能在匿名方法、lambda表达式或查询表达式内使用in ref或out参数“”下面是一个简单的例子：private void Foo(){    int value;  ...

问不能在lambda表达式中使用ref或out参数
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