为什么VAR计算为System.Object中的＆QUOT;的foreach（在table.Rows VAR行）QUOT;？ [英] Why does var evaluate to System.Object in "foreach (var row in table.Rows)"?
问题描述
当我进入这个的foreach 语句...
When I enter this foreach statement...
foreach (var row in table.Rows)
...工具提示为无功说类System.Object的
我很困惑，为什么这不是类的System.Data.DataRow 。
I'm confused why it's not class System.Data.DataRow.
（如果你想知道，是的，我有使用System.Data这我的code文件的顶部。）
(In case you're wondering, yes, I have using System.Data at the top of my code file.)
如果我宣布了明确的类型，如...
If I declare the type explicitly, as in...
foreach (DataRow row in table.Rows)
...它工作正常，没有错误。
...it works fine with no errors.
另外，如果我做的......
Also if I do...
var numbers = new int[] { 1, 2, 3 };
foreach (var number in numbers)
... VAR的计算结果为结构System.Int32的。所以，问题不在于 VAR 在的foreach 子句不起作用。
...var evaluates to struct System.Int32. So, the problem is not that var doesn't work in a foreach clause.
所以，有一些奇怪的 DataRowCollection ，其中的项目不会自动计算为的DataRow 。但我无法弄清楚它是什么。有没有人有一个解释？
So, there's something strange about DataRowCollection where the items don't automatically evaluate to DataRow. But I can't figure out what it is. Does anyone have an explanation?
更新
我真的撕裂这回答标记（codeKA和Oliver）......最后，我决定以纪念codeKA的，因为它真实地回答我的问题，但奥利弗回答我应该是问题问：）
I was really torn which answer to mark (Codeka and Oliver)...In the end, I decided to mark Codeka's because it truly answers my question, but Oliver answers the question I should have been asking :)
推荐答案
这是因为，<一个href="http://msdn.microsoft.com/en-us/library/system.data.datarowcollection%28v=VS.100%29.aspx">DataRowCollection类只能实现的IEnumerable 的非通用版本。因此，编译器不知道该变量的类型。
That's because the DataRowCollection class only implements the non-generic version of IEnumerable. So the compiler doesn't know what the type of the variable is.
通过明确地把类型在那里，你基本上告诉编译器生成一个明确的转换，从对象到的DataRow 。
By explicitly putting the type in there, you basically tell the compiler to generate an explicit cast from object to DataRow.
这是一个问题，你会发现有许多加回在.NET 1.x的天藏品和类，仿制药可用了。
This is a problem you'll find with many of the collections and classes added back in the .NET 1.x days, before generics were available.
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