blocks|key|1013737|text|生成的可枚举序列的类型由select子句后的表达式类型确定，因此：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1013738|select+Tuple.Create(
++++B.Key,
++++(from+A+in+As+where+A.F+==+B.Key+select+A).ToList()
)|code-block|syntax|javascript|1013739|entityMap^0|C|6|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|$]]

The type of the enumerable sequence produced is determined by the type of the expression after the <code>select</code> clause, so:

<pre><code>select Tuple.Create(
 B.Key,
 (from A in As where A.F == B.Key select A).ToList()
)
</code></pre>

blocks|key|868232|text|Tuple<String,+IEnumerable<MyType>>+<=>+Tuple<String,+MyType>开始时，但是问题不在这里，您不能将匿名类型转换为Tuple。您必须显式定义类型，然后使用它。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|868233|public+class+YourClass
{
++++public+string+F1+{get;+set;}
++++public+IEnumerable<MyType>+F2+{get;+set;}
}+

IEnumerable<YourClass>+result
++=+from+A+in+As
++++group+A+by+A.F+into+B
++++select+new+YourClass
++++{
++++++F1+=+B.Key,
++++++F2+=+from+A+in+As
+++++++++++where+A.F+==+B.Key
+++++++++++select+A
++++};|code-block|syntax|javascript|868234|entityMap^0|0|1O|2C|5|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

<code>Tuple&lt;String, IEnumerable&lt;MyType&gt;&gt; &lt;=&gt; Tuple&lt;String, MyType&gt;</code> this at first, but problem not here, you cant cast anonymous type to <code>Tuple</code>. You must explicitly define type then use it.



<pre><code>public class YourClass
{
 public string F1 {get; set;}
 public IEnumerable&lt;MyType&gt; F2 {get; set;}
} 

IEnumerable&lt;YourClass&gt; result
 = from A in As
 group A by A.F into B
 select new YourClass
 {
 F1 = B.Key,
 F2 = from A in As
 where A.F == B.Key
 select A
 };
</code></pre>

blocks|key|1013764|text|由于要使用select+{.}创建匿名类型，所以必须使用var。没有办法显式地表示类型。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1013765|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|$]]

Since you're creating an anonymous type with the select new {... } you have to use var. There is no way to express the type explicitly.

blocks|key|868774|text|不能显式声明类型，因为|type|unstyled|depth|inlineStyleRanges|entityRanges|data|868775|select+new+{
+++Member+=+Value
}|code-block|syntax|javascript|868776|您使用的是匿名类型--这类类型有无法形容的名称，因此这是必须使用var的情况之一。|offset|length|style|BOLD|CODE|868777|entityMap^0|0|0|5|4|W|3|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Q|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|R|8|@$I|S|J|T|K|L]|$I|U|J|V|K|M]]|9|@]|A|$]]|$1|N|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|O|$]]

You can't explicitly declare the type because by saying

<pre><code>select new {
 Member = Value
}
</code></pre>

you're using an anonymous type - such types have unspeakable names and so this is one of the cases where you must use <code>var</code>.

blocks|key|811785|text|尽管您知道对象“内部”是相同的，但是C#是静态类型的，并且根据它们的元数据(名称、命名空间.)而不是它们的成员来解析类型。您选择的是匿名类型，而不是Tuple，因此类型解析器不能“同意”将其用作Tuple。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|811786|如果您悬停在Visual中的var关键字上，它将告诉您它是什么类型(因为它必须在编译时知道，除非它是dynamic)。但是，由于您使用的是匿名类型，您将无法显式地编写该类型--它在C#源代码中没有名称。|811787|您可以做的是在其他地方定义类型。|811788|internal+class+MyObj
{
++++public+MyObj(string+head,+IEnumerable<Foo>+tail)
++++{
++++++++Head+=+head;
++++++++Tail+=+tail;
++++}

++++public+string+Head+{+get;+set;+}
++++public+IEnumerable<Foo>+Tail+{+get;+set;+}
}|code-block|syntax|javascript|811789|然后在查询中使用它：|811790|IEnumerable<MyObj>+result
++=+from+A+in+As
++++group+A+by+A.F+into+B
++++select+new+MyObj(
++++++++B.Key,
++++++++from+A+in+As
++++++++where+A.F+==+B.Key
++++++++select+A);|811791|或者按照乔恩的建议使用Tuple，here。|811792|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/14359066/1659828^0|22|5|2P|5|0|E|3|1E|7|0|0|0|0|0|B|5|H|4|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|17|8|@$9|18|A|19|B|C]|$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1C|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|1D|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1E|8|@]|D|@]|E|$]]|$1|Q|3|R|5|L|7|1F|8|@]|D|@]|E|$M|N]]|$1|S|3|T|5|6|7|1G|8|@$9|1H|A|1I|B|C]]|D|@$9|1J|A|1K|1|1L]]|E|$]]|$1|U|3|-4|5|6|7|1M|8|@]|D|@]|E|$]]]|V|$W|$5|X|Y|Z|E|$10|11]]]]

Although you know that the object "insides" are the same, C# is statically typed and resolves types based on their metadata (name, namespace...), not on their members. You select an anonymous type, not a <code>Tuple</code>, so the type resolver cannot "agree" with it being used as a <code>Tuple</code>.

If you hover over the <code>var</code> keyword in Visual Studio, it will tell you what type is it (because it must be known during compile time, unless it's a <code>dynamic</code>). However due to the fact you are using anonymous type, you will not be able to write the type explicitly - it has no name in the C# source code.

What you might do is either define the type elsewhere

<pre><code>internal class MyObj
{
 public MyObj(string head, IEnumerable&lt;Foo&gt; tail)
 {
 Head = head;
 Tail = tail;
 }

 public string Head { get; set; }
 public IEnumerable&lt;Foo&gt; Tail { get; set; }
}
</code></pre>

and then use it in your query:

<pre><code>IEnumerable&lt;MyObj&gt; result
 = from A in As
 group A by A.F into B
 select new MyObj(
 B.Key,
 from A in As
 where A.F == B.Key
 select A);
</code></pre>

or use a <code>Tuple</code> as Jon suggested <a href="https://stackoverflow.com/a/14359066/1659828">here</a>.

I'm doing the following request. It works as supposed to and returns data structured correctly. (It creates an element with "head" corresponding to the common field and puts the all elements of the same value in that field as a an Array in the "tail".)

<pre><code>var result
 = from A in As
 group A by A.F into B
 select new 
 {
 F1 = B.Key,
 F2 = from A in As
 where A.F == B.Key
 select A
 };
</code></pre>

Now I'd like to declare it's type explicitly. I've checked in the debugger that my assumption on types is correct, however, when I try to declare that, it gives me conversion errors.

<ol>
<li>Why?</li>
<li>How can I declare the type explicitly?</li>
</ol>

I've tried different variant of declarations and as but failed.

<pre><code>IEnumerable&lt;Tuple&lt;String, IEnumerable&lt;MyType&gt;&gt;&gt; result 
 = from ...
 } as Tuple&lt;String, MyType&gt;;
</code></pre>

I know it's doable but I lack the experience to get it right. I've noticed that the following works. However, I'm not sure how to take it a step further, exchanging Object for the actual variable type.

<pre><code>IEnumerable&lt;Object&gt; result 
 = from ...
 } as Object;
</code></pre>

Declaring explicit type instead of var in select statement

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在做下面的请求。它的工作方式应该是正确的，并返回结构正确的数据。(它创建一个与公共字段对应的"head“元素，并将该字段中值相同的所有元素作为数组放在”tail“中。)var result  = from A in As    group A by A.F into B    select new     {   ...

问在select语句中声明显式类型而不是var
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问在select语句中声明显式类型而不是varEN