The type 'X' does not exist in the type 'Y.Z'

Question

Our team has recently migrated from Visual Studio 2008/.NET3.5 to Visual Studio 2010/.NET4.0. Now, VS2010 gives me a strange error message. It's reproducible with the following program:

using System;

namespace Some.Main
{
}

namespace SomeLib
{
    interface Some
    {
    }
}

namespace ConsoleApplication1
{
    using Some.Main;
    using SomeLib;

    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Press enter to continue");
            Console.ReadLine();
        }
    }
}

This worked just fine in VS2008, but in VS2010 I get the following error message:

The type name 'Main' does not exist in the type 'SomeLib.Some'

Interestingly, if I hit 'Build Solution', the program builds just fine, and I can even execute it without any problems. It's just Visual Studio that seems to have a problem with this code.

Unfortunately, I'm working on a large-ish legacy application and I cannot (easily) change the names of these namespaces.

I'd like to know how I can fix this error, and I'm also curious what causes it.

It's funny. That exact code, compiles on Mono (latest). But on Visual Studio 2010, it doesn't — Michael Buen, Jun 05 '12 at 09:10
@MichaelBuen It's even worse, because on Visual Studio 2008, it also compiles. — jqno, Jun 05 '12 at 09:12
ideone uses Mono for its C#. See your code here, compiles fine http://ideone.com/zmLCO — Michael Buen, Jun 05 '12 at 09:13
perhaps asking Eric Lippert is a good idea. He could explain the discrepancy — Michael Buen, Jun 05 '12 at 09:14
@jqno I think you've found a bug on Visual Studio 2010 ツ Language-wise, your code is perfectly valid, it even builds — Michael Buen, Jun 05 '12 at 09:19

score 9 · Accepted Answer · edited May 23 '17 at 11:51

You simply make the editor confused. Some is both a namespace and an interface name, evidently it doesn't check/parse usings in the order they're declared.

If you want to make clear you're referring to the namespace and not the type name simply add global:: to the using declaration (to start from the root namespace), like this:

using global::Some.Main;

UPDATE
Very good post here on SO linked by @alex in a comment: Should 'using' statements be inside or outside the namespace?

score 4 · Answer 2 · answered Jun 05 '12 at 09:10

4

I think IntelliSense is confused by the naming and doesn't "understand" who's who.

Attached screenshot demonstrates what's going on: IntelliSense "thinks" Some.Main refers to the interface named Some, probably because there isn't a namespace called Some anywhere.

Luckily, the compiler isn't fooled like that and the code seems to work just fine, like you said.

IntelliSense being fooled

answered Jun 05 '12 at 09:10

Alex

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And after you do a build, IntelliSense stops complaining too. – H H Jun 05 '12 at 09:14
@HenkHolterman Until you make a change; then it comes back :). – jqno Jun 05 '12 at 09:17
@HenkHolterman And that's more funny, I tried building it, it compiles. Yet it has error when you make changes to code. Are the Visual Studio IDE team and C# compiler team a separate team? – Michael Buen Jun 05 '12 at 09:18
1

@MichaelBuen I guess they're but more than that they use pretty different techniques to parse code. For Intellisense they key point is speed and error-tolerance. – Adriano Repetti Jun 05 '12 at 09:34

score 1 · Answer 3 · answered Jun 05 '12 at 08:58

1

Try this:

using Some.Main;
using SomeLib;

namespace ConsoleApplication1
{
    // instead of placing usings here.
}

answered Jun 05 '12 at 08:58

abatishchev

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Beware, moving `using`s around might lead to code breaking and should *not* be done blindly! See http://stackoverflow.com/questions/125319/should-usings-be-inside-or-outside-the-namespace – Alex Jun 05 '12 at 09:45
@alex: however I always place using out of namespace and never hear any problems. – abatishchev Jun 05 '12 at 10:36

The type 'X' does not exist in the type 'Y.Z'

3 Answers3