blocks|key|225582|text|这里的问题是，您定义了一个匿名方法，该方法返回一个string，但试图将其直接分配给一个string。它是一个表达式，当它被调用时会产生一个string，它不是一个直接的string。需要将其分配给兼容的委托类型。在这种情况下，最简单的选择是Func<string>|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|225583|Func<string>+temp+=+()+=>+{return+"test";};|code-block|syntax|javascript|225584|这可以通过转换或使用委托构造函数在一行代码中建立lambda的类型，然后调用来完成。|225585|string+temp+=+((Func<string>)(()+=>+{+return+"test";+}))();
string+temp+=+new+Func<string>(()+=>+{+return+"test";+})();|225586|注意:两个样本都可以简称为缺少{+return+...+}的表达形式|225587|Func<string>+temp+=+()+=>+"test";
string+temp+=+((Func<string>)(()+=>+"test"))();
string+temp+=+new+Func<string>(()+=>+"test")();|225588|entityMap^0|P|6|18|6|1Y|6|2D|6|3D|C|0|0|0|0|F|E|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|16|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|17|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|18|8|@$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|S|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|T|$]]

The problem here is that you've defined an anonymous method which returns a <code>string</code> but are trying to assign it directly to a <code>string</code>. It's an expression which when invoked produces a <code>string</code> it's not directly a <code>string</code>. It needs to be assigned to a compatible delegate type. In this case the easiest choice is <code>Func&lt;string&gt;</code>

<pre><code>Func&lt;string&gt; temp = () =&gt; {return "test";};
</code></pre>

This can be done in one line by a bit of casting or using the delegate constructor to establish the type of the lambda followed by an invocation.

<pre><code>string temp = ((Func&lt;string&gt;)(() =&gt; { return "test"; }))();
string temp = new Func&lt;string&gt;(() =&gt; { return "test"; })();
</code></pre>

Note: Both samples could be shorted to the expression form which lacks the <code>{ return ... }</code>

<pre><code>Func&lt;string&gt; temp = () =&gt; "test";
string temp = ((Func&lt;string&gt;)(() =&gt; "test"))();
string temp = new Func&lt;string&gt;(() =&gt; "test")();
</code></pre>

blocks|key|3098854|text|您正在尝试将函数委托分配给字符串类型。试试这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3098855|Func<string>+temp+=+()+=>+{return+"test";};|code-block|syntax|javascript|3098856|您现在可以按如下方式执行函数：|3098857|string+s+=+temp();|3098858|"s“变量现在将具有值"test”。|3098859|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 are attempting to assign a function delegate to a string type. Try this:

<pre><code>Func&lt;string&gt; temp = () =&gt; {return "test";};
</code></pre>

You can now execute the function thusly:

<pre><code>string s = temp();
</code></pre>

The "s" variable will now have the value "test".

blocks|key|229152|text|使用一些辅助函数和泛型，您可以让编译器推断类型，并将其缩短一点：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|229153|public+static+TOut+FuncInvoke<TOut>(Func<TOut>+func)
{
++++return+func();
}

var+temp+=+FuncInvoke(()=>"test");|code-block|syntax|javascript|229154|附注:这也很好，因为你可以返回一个匿名类型：|229155|var+temp+=+FuncInvoke(()=>new+{foo=1,bar=2});|229156|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Using a little helper function and generics you can let the compiler infer the type, and shorten it a little bit:

<pre><code>public static TOut FuncInvoke&lt;TOut&gt;(Func&lt;TOut&gt; func)
{
 return func();
}

var temp = FuncInvoke(()=&gt;"test");
</code></pre>

Side note: this is also nice as you then are able to return an anonymous type:

<pre><code>var temp = FuncInvoke(()=&gt;new {foo=1,bar=2});
</code></pre>

blocks|key|3098904|text|您可以使用带参数的匿名方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3098905|int+arg+=+5;

string+temp+=+((Func<int,+string>)((a)+=>+{+return+a+==+5+?+"correct"+:+"not+correct";+}))(arg);|code-block|syntax|javascript|3098906|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|$]]

you can use anonymous method with argument :

<pre><code>int arg = 5;

string temp = ((Func&lt;int, string&gt;)((a) =&gt; { return a == 5 ? "correct" : "not correct"; }))(arg);
</code></pre>

blocks|key|2884970|text|匿名方法可以使用函数委托返回值。下面是我展示了如何使用匿名方法返回值的示例。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2884971|using+System;
using+System.Collections.Generic;
using+System.Linq;
using+System.Text;
using+System.Threading.Tasks;

namespace+ConsoleApp1
{
++++class+Program
++++{


++++++++static+void+Main(string[]+args)
++++++++{
++++++++++++Func<int,+int>+del+=+delegate+(int+x)
++++++++++++++{
++++++++++++++++++return+x+*+x;

++++++++++++++};

++++++++++++int+p=+del(4);
++++++++++++Console.WriteLine(p);
++++++++++++Console.ReadLine();
++++++++}
++++}
}|code-block|syntax|javascript|2884972|entityMap^0|0|12|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

An anonymous method can return a value using a func delegate.
Here is an example where I have shown how to return a value using an anonymous method.

<pre><code>using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
 class Program
 {


 static void Main(string[] args)
 {
 Func&lt;int, int&gt; del = delegate (int x)
 {
 return x * x;

 };

 int p= del(4);
 Console.WriteLine(p);
 Console.ReadLine();
 }
 }
}
</code></pre>

blocks|key|225648|text|这是使用C#+8的另一个示例(也可以与支持并行任务的其他.NET版本一起使用)|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|225649|using+System;
using+System.Threading.Tasks;

namespace+Exercise_1_Creating_and_Sharing_Tasks
{
++++internal+static+class+Program
++++{
++++++++private+static+int+TextLength(object+o)
++++++++{
++++++++++++Console.WriteLine($"Task+with+id+{Task.CurrentId}+processing+object+{o}");
++++++++++++return+o.ToString().Length;
++++++++}

++++++++private+static+void+Main()
++++++++{
++++++++++++const+string+text1+=+"Welcome";
++++++++++++const+string+text2+=+"Hello";

++++++++++++var+task1+=+new+Task<int>(()+=>+TextLength(text1));
++++++++++++task1.Start();

++++++++++++var+task2+=+Task.Factory.StartNew(TextLength,+text2);

++++++++++++Console.WriteLine($"Length+of+'{text1}'+is+{task1.Result}");
++++++++++++Console.WriteLine($"Length+of+'{text2}'+is+{task2.Result}");

++++++++++++Console.WriteLine("Main+program+done");
++++++++++++Console.ReadKey();
++++++++}
++++}
}|code-block|syntax|javascript|225650|entityMap^0|4|4|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

This is another example using C# 8 (could also work with other .NET versions supporting parallel tasks)

<pre class="lang-cs prettyprint-override"><code>using System;
using System.Threading.Tasks;

namespace Exercise_1_Creating_and_Sharing_Tasks
{
 internal static class Program
 {
 private static int TextLength(object o)
 {
 Console.WriteLine($"Task with id {Task.CurrentId} processing object {o}");
 return o.ToString().Length;
 }

 private static void Main()
 {
 const string text1 = "Welcome";
 const string text2 = "Hello";

 var task1 = new Task&lt;int&gt;(() =&gt; TextLength(text1));
 task1.Start();

 var task2 = Task.Factory.StartNew(TextLength, text2);

 Console.WriteLine($"Length of '{text1}' is {task1.Result}");
 Console.WriteLine($"Length of '{text2}' is {task2.Result}");

 Console.WriteLine("Main program done");
 Console.ReadKey();
 }
 }
}
</code></pre>

This fails 

<pre><code>string temp = () =&gt; {return "test";};
</code></pre>

with the error

<blockquote>
 Cannot convert lambda expression to type 'string' because it is not a delegate type
</blockquote>

What does the error mean and how can I resolve it?

How to return value with anonymous method?

编译器

此操作失败string temp = () => {return "test";};带着错误无法将lambda表达式转换为类型“string”，因为它不是委托类型这个错误是什么意思，我如何解决它？

问如何使用匿名方法返回值？
EN

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