title: open c# namespace from same solution, referenced project in f#
body: <p>I am still trying to get my head around namespaces in referenced projects.</p>
  
  <p>I have a c# project where a namespace ("A") is defined.
  I create a F# application, where I reference the c# project.</p>
  
  <pre><code>open A
  </code></pre>
  
  <p>leads to the following:</p>
  
  <blockquote>
    <p>error FS0039: The namespace or module 'A' is not defined</p>
  </blockquote>
  
  <p>This is what I have checked:</p>
  
  <ul>
  <li>The C# and F# project target the same framework (.Net Framework 4.5) (<a href="https://stackoverflow.com/questions/6091132/f-the-namespace-or-module-xxxx-is-not-defined">F# the namespace or module &#39;XXXX&#39; is not defined</a>)</li>
  <li>The C# and F# project have the same target (Any CPU)</li>
  <li>The C# project is correctly listed among the F# project references</li>
  <li>I am correctly trying to open a namespace (not as in this case: <a href="https://stackoverflow.com/questions/3901805/how-to-use-c-sharp-object-from-f">How to use C# object from F#?</a>)</li>
  <li>I am not operating from the FSI (<a href="https://connect.microsoft.com/VisualStudio/feedback/details/632859/difference-in-namespace-reference-between-f-interactive-and-compiled-exe" rel="nofollow noreferrer">https://connect.microsoft.com/VisualStudio/feedback/details/632859/difference-in-namespace-reference-between-f-interactive-and-compiled-exe</a>)</li>
  </ul>
  
  <p>MSDN is not much of a help (<a href="http://msdn.microsoft.com/en-us/library/vstudio/dd393787.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/vstudio/dd393787.aspx</a>).</p>
  
  <p>Thanks.</p>
  
  <p>[EDIT] </p>
  
  <p>I have started from scratch, so that the example is lean and clean.</p>
  
  <p>The C# project "ClassLibrary1" contains:</p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  using System.Threading.Tasks;
  
  namespace ClassLibrary1
  {
      public class Class1
      {
      }
  }
  </code></pre>
  
  <p>The F# Application is:</p>
  
  <pre><code>// Learn more about F# at http://fsharp.net
  // See the 'F# Tutorial' project for more help.
  open ClassLibrary1
  
  [&lt;EntryPoint&gt;]
  let main argv = 
      printfn "%A" argv
      0 // return an integer exit code
  </code></pre>
  
  <p>The error: </p>
  
  <blockquote>
    <p>The namespace or module 'ClassLibrary1' is not defined</p>
  </blockquote>