open c# namespace from same solution, referenced project in f#

Question

I am still trying to get my head around namespaces in referenced projects.

I have ac# project where a namespace ("A") is defined. I create a F# application, where I reference the c# project.

open A

leads to the following:

error FS0039: The namespace or module 'A' is not defined

This is what I have checked:

• The C# and F# project target the same framework (.Net Framework 4.5) ( F# the namespace or module 'XXXX' is not defined )
• The C# and F# project have the same target (Any CPU)
• The C# project is correctly listed among the F# project references
• I am correctly trying to open a namespace (not as in this case: How to use C# object from F#? )
• I am not operating from the FSI ( https://connect.microsoft.com/VisualStudio/feedback/details/632859/difference-in-namespace-reference-between-f-interactive-and-compiled-exe )

MSDN is not much of a help ( http://msdn.microsoft.com/en-us/library/vstudio/dd393787.aspx ).

Thanks.

[EDIT]

I have started from scratch, so that the example is lean and clean.

The C# project "ClassLibrary1" contains:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ClassLibrary1
{
    public class Class1
    {
    }
}

The F# Application is:

// Learn more about F# at http://fsharp.net
// See the 'F# Tutorial' project for more help.
open ClassLibrary1

[<EntryPoint>]
let main argv = 
    printfn "%A" argv
    0 // return an integer exit code

The error:

The namespace or module 'ClassLibrary1' is not defined

Answer 1

Make sure your reference is a real project references and not just referencing the DLL in the bin\\Debug folder.

If you can't get a real project reference to work, make sure the F# project is set to depend on the C# project so that it gets built first by Visual Studio (right-click on the project and go to Project Dependencies then use the tickboxes).

Answer 2

I had this same issue. All I had to do was make sure my C# project dependencies were all settled, build my C# projects, then the F# project was able to reference the correct dll's.

In Visual Studio, you can right click on each C# project and press build. In VSCode, you have to use the terminal to navigate to each project and run dotnet build .