blocks|key|4583596|text|这很可能是因为没有闭包，例如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4583597|int+age+=+25;
Action<string>+withClosure+=+s+=>+Console.WriteLine("My+name+is+{0}+and+I+am+{1}+years+old",+s,+age);
Action<string>+withoutClosure+=+s+=>+Console.WriteLine("My+name+is+{0}",+s);
Console.WriteLine(withClosure.Method.IsStatic);
Console.WriteLine(withoutClosure.Method.IsStatic);|code-block|syntax|javascript|4583598|这将输出withClosure的false和withoutClosure的true。|offset|length|style|CODE|4583599|当你使用lambda表达式时，编译器会创建一个小类来包含你的方法，这将编译成如下所示(实际的实现很可能略有不同)：|4583600|private+class+<Main>b__0
{
++++public+int+age;
++++public+void+withClosure(string+s)
++++{
++++++++Console.WriteLine("My+name+is+{0}+and+I+am+{1}+years+old",+s,+age)
++++}
}

private+static+class+<Main>b__1
{
++++public+static+void+withoutClosure(string+s)
++++{
++++++++Console.WriteLine("My+name+is+{0}",+s)
++++}
}

public+static+void+Main()
{
++++var+b__0+=+new+<Main>b__0();
++++b__0.age+=+25;
++++Action<string>+withClosure+=+b__0.withClosure;
++++Action<string>+withoutClosure+=+<Main>b__1.withoutClosure;
++++Console.WriteLine(withClosure.Method.IsStatic);
++++Console.WriteLine(withoutClosure.Method.IsStatic);
}|4583601|您可以看到生成的Action<string>实例实际上指向这些生成的类上的方法。|4583602|entityMap^0|0|0|4|B|G|5|M|E|11|4|0|0|0|8|E|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@$I|X|J|Y|K|L]|$I|Z|J|10|K|L]|$I|11|J|12|K|L]|$I|13|J|14|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|17|8|@$I|18|J|19|K|L]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|T|$]]

<p>This is most likely because there are no closures, for example:</p>

<pre><code>int age = 25;
Action&lt;string&gt; withClosure = s =&gt; Console.WriteLine("My name is {0} and I am {1} years old", s, age);
Action&lt;string&gt; withoutClosure = s =&gt; Console.WriteLine("My name is {0}", s);
Console.WriteLine(withClosure.Method.IsStatic);
Console.WriteLine(withoutClosure.Method.IsStatic);
</code></pre>

<p>This will output <code>false</code> for <code>withClosure</code> and <code>true</code> for <code>withoutClosure</code>.</p>

<p>When you use a lambda expression, the compiler creates a little class to contain your method, this would compile to something like the following (the actual implementation most likely varies slightly):</p>

<pre><code>private class &lt;Main&gt;b__0
{
    public int age;
    public void withClosure(string s)
    {
        Console.WriteLine("My name is {0} and I am {1} years old", s, age)
    }
}

private static class &lt;Main&gt;b__1
{
    public static void withoutClosure(string s)
    {
        Console.WriteLine("My name is {0}", s)
    }
}

public static void Main()
{
    var b__0 = new &lt;Main&gt;b__0();
    b__0.age = 25;
    Action&lt;string&gt; withClosure = b__0.withClosure;
    Action&lt;string&gt; withoutClosure = &lt;Main&gt;b__1.withoutClosure;
    Console.WriteLine(withClosure.Method.IsStatic);
    Console.WriteLine(withoutClosure.Method.IsStatic);
}
</code></pre>

<p>You can see the resulting <code>Action&lt;string&gt;</code> instances actually point to methods on these generated classes.</p>


blocks|key|4583651|text|该方法没有闭包，而且还引用了静态方法本身(Console.WriteLine)，所以我希望它是静态的。该方法将为闭包声明一个封闭匿名类型，但在此实例中不是必需的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4583652|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

<p>The method has no closures and also references a static method itself (Console.WriteLine), so I would expect it to be static. The method will declare an enclosing anonymous type for a closure, but in this instance it is not required.</p>


blocks|key|4583697|text|在Roslyn中更改了委派缓存行为。以前，如上所述，任何没有捕获变量的lambda表达式都会在调用点被编译成static方法。Roslyn改变了这种行为。现在，任何捕获变量或不捕获变量的lambda都被转换为一个显示类：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4583698|在这个例子中：|4583699|public+class+C
{
++++public+void+M()
++++{
++++++++var+x+=+5;
++++++++Action<int>+action+=+y+=>+Console.WriteLine(y);
++++}
}|code-block|syntax|javascript|4583700|本机编译器输出：|4583701|public+class+C
{
++++[CompilerGenerated]
++++private+static+Action<int>+CS$<>9__CachedAnonymousMethodDelegate1;
++++public+void+M()
++++{
++++++++if+(C.CS$<>9__CachedAnonymousMethodDelegate1+==+null)
++++++++{
++++++++++++C.CS$<>9__CachedAnonymousMethodDelegate1+=+new+Action<int>(C.<M>b__0);
++++++++}
++++++++Action<int>+arg_1D_0+=+C.CS$<>9__CachedAnonymousMethodDelegate1;
++++}
++++[CompilerGenerated]
++++private+static+void+<M>b__0(int+y)
++++{
++++++++Console.WriteLine(y);
++++}
}|4583702|罗斯林：|4583703|public+class+C
{
++++[CompilerGenerated]
++++private+sealed+class+<>c__DisplayClass0
++++{
++++++++public+static+readonly+C.<>c__DisplayClass0+CS$<>9__inst;
++++++++public+static+Action<int>+CS$<>9__CachedAnonymousMethodDelegate2;
++++++++static+<>c__DisplayClass0()
++++++++{
++++++++++++//+Note:+this+type+is+marked+as+'beforefieldinit'.
++++++++++++C.<>c__DisplayClass0.CS$<>9__inst+=+new+C.<>c__DisplayClass0();
++++++++}
++++++++internal+void+<M>b__1(int+y)
++++++++{
++++++++++++Console.WriteLine(y);
++++++++}
++++}
++++public+void+M()
++++{
++++++++Action<int>+arg_22_0;
++++++++if+(arg_22_0+=+C.
+++++++++++++++++++++++<>c__DisplayClass0.CS$<>9__CachedAnonymousMethodDelegate2+==+null)
++++++++{
++++++++++++C.<>c__DisplayClass0.CS$<>9__CachedAnonymousMethodDelegate2+=
++++++++++new+Action<int>(C.<>c__DisplayClass0.CS$<>9__inst.<M>b__1);
++++++++}
++++}
}|4583704|Delegate+caching+behavior+changes+in+Roslyn谈到了为什么要做出这样的改变。|4583705|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/30897647/delegate-caching-behavior-changes-in-roslyn^0|1I|6|0|0|0|0|0|0|0|0|17|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@$9|15|A|16|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|17|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|18|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|19|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1A|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1B|8|@]|D|@]|E|$]]|$1|S|3|T|5|J|7|1C|8|@]|D|@]|E|$K|L]]|$1|U|3|V|5|6|7|1D|8|@]|D|@$9|1E|A|1F|1|1G]]|E|$]]|$1|W|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]]|X|$Y|$5|Z|10|11|E|$12|13]]]]

<p>Delegate caching behavior was changed in Roslyn. Previously, as stated, any lambda expression which didn't capture variables was compiled into a <code>static</code> method at the call site. Roslyn changed this behavior. Now, any lambda, which captures variables or not, is transformed into a display class:</p>

<p>Given this example:</p>

<pre><code>public class C
{
    public void M()
    {
        var x = 5;
        Action&lt;int&gt; action = y =&gt; Console.WriteLine(y);
    }
}
</code></pre>

<p>Native compiler output:</p>

<pre><code>public class C
{
    [CompilerGenerated]
    private static Action&lt;int&gt; CS$&lt;&gt;9__CachedAnonymousMethodDelegate1;
    public void M()
    {
        if (C.CS$&lt;&gt;9__CachedAnonymousMethodDelegate1 == null)
        {
            C.CS$&lt;&gt;9__CachedAnonymousMethodDelegate1 = new Action&lt;int&gt;(C.&lt;M&gt;b__0);
        }
        Action&lt;int&gt; arg_1D_0 = C.CS$&lt;&gt;9__CachedAnonymousMethodDelegate1;
    }
    [CompilerGenerated]
    private static void &lt;M&gt;b__0(int y)
    {
        Console.WriteLine(y);
    }
}
</code></pre>

<p>Roslyn:</p>

<pre><code>public class C
{
    [CompilerGenerated]
    private sealed class &lt;&gt;c__DisplayClass0
    {
        public static readonly C.&lt;&gt;c__DisplayClass0 CS$&lt;&gt;9__inst;
        public static Action&lt;int&gt; CS$&lt;&gt;9__CachedAnonymousMethodDelegate2;
        static &lt;&gt;c__DisplayClass0()
        {
            // Note: this type is marked as 'beforefieldinit'.
            C.&lt;&gt;c__DisplayClass0.CS$&lt;&gt;9__inst = new C.&lt;&gt;c__DisplayClass0();
        }
        internal void &lt;M&gt;b__1(int y)
        {
            Console.WriteLine(y);
        }
    }
    public void M()
    {
        Action&lt;int&gt; arg_22_0;
        if (arg_22_0 = C.
                       &lt;&gt;c__DisplayClass0.CS$&lt;&gt;9__CachedAnonymousMethodDelegate2 == null)
        {
            C.&lt;&gt;c__DisplayClass0.CS$&lt;&gt;9__CachedAnonymousMethodDelegate2 =
          new Action&lt;int&gt;(C.&lt;&gt;c__DisplayClass0.CS$&lt;&gt;9__inst.&lt;M&gt;b__1);
        }
    }
}
</code></pre>

<p><a href="https://stackoverflow.com/questions/30897647/delegate-caching-behavior-changes-in-roslyn">Delegate caching behavior changes in Roslyn</a> talks about why this change was made.</p>


blocks|key|77060|text|从C#+6开始，这将始终默认为实例方法，并且永远不会是静态的(因此actionMethod.Method.IsStatic将始终为false)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|77061|查看此处：Why+has+a+lambda+with+no+capture+changed+from+a+static+in+C#+5+to+an+instance+method+in+C#+6?|77062|这里：Difference+in+CSC+and+Roslyn+compiler's+static+lambda+expression+evaluation?|77063|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/33948144/why-has-a-lambda-with-no-capture-changed-from-a-static-in-c-sharp-5-to-an-instan|1|https://stackoverflow.com/questions/31408767/difference-in-csc-and-roslyn-compilers-static-lambda-expression-evaluation/31411479#31411479^0|X|S|0|5|2L|0|0|3|24|1|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|H|3|I|5|6|7|10|8|@]|D|@$9|11|A|12|1|13]]|E|$]]|$1|J|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|K|$L|$5|M|N|O|E|$P|Q]]|R|$5|M|N|O|E|$P|S]]]]

<p>As of C# 6, this will always default to instance methods now, and will never be static (so <code>actionMethod.Method.IsStatic</code> will always be false). </p>

<p>See here: <a href="https://stackoverflow.com/questions/33948144/why-has-a-lambda-with-no-capture-changed-from-a-static-in-c-sharp-5-to-an-instan">Why has a lambda with no capture changed from a static in C# 5 to an instance method in C# 6?</a></p>

<p>and here: <a href="https://stackoverflow.com/questions/31408767/difference-in-csc-and-roslyn-compilers-static-lambda-expression-evaluation/31411479#31411479">Difference in CSC and Roslyn compiler&#39;s static lambda expression evaluation?</a></p>


<p>As you can see in the code below, I have declared an <code>Action&lt;&gt;</code> object as a variable.</p>

<p>Would anybody please let me know why this action method delegate behaves like a static method? </p>

<p>Why does it return <code>true</code> in the following code?</p>

<h2>Code:</h2>

<pre><code>public static void Main(string[] args)
{
    Action&lt;string&gt; actionMethod = s =&gt; { Console.WriteLine("My Name is " + s); };

    Console.WriteLine(actionMethod.Method.IsStatic);

    Console.Read();
}
</code></pre>

<h2>Output:</h2>

<p><img src="https://i.stack.imgur.com/qwtFk.png" alt="example output of sample"></p>


Why do some C# lambda expressions compile to static methods?

编译器

正如您在下面的代码中看到的，我已经将一个Action<>对象声明为一个变量。谁能让我知道为什么这个action方法委托的行为像一个静态方法？为什么它在下面的代码中返回true？代码：public static void Main(string[] args){    Action<string> actionMetho...

问为什么一些C#λ表达式会编译成静态方法？
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问为什么一些C#λ表达式会编译成静态方法？
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