title: How can I Import A Namespace from A File in A Seperate Folder in C#
body: <p>How do I bring into the current namespace an extension method (see below) into scope, when the file this class is defined in is in another folder? </p>
  
  <p>When <code>StringHandler.cs</code> is in the <code>Product</code> folder, I can include <code>using Utilities;</code> in <code>Product.cs</code>, but when it is in a separate folder, alongside the <code>Project</code> folder (in the <code>Utilities</code> folder), I can't figure out how to include it. Can someone please explain how I can use the using keyword in this case? For instance, where is <code>using</code> really pointing to on my file system (do I need to specify the using directory relative to my <code>csproj</code> file or to my <code>CallCenter.sln</code> file?)?</p>
  
  <pre><code>│   CallCenter.sln
  │
  ├───src
  │   ├───Project
  │   │   │   Product.cs
  |   |   |   Project.csproj
  │   │   ├───bin
  │   │   │   └───...
  │   │   │
  │   │   └───obj
  │   │       └───...         
  │   │
  │   └───Utilities
  │           StringHandler.cs
  </code></pre>
  
  <p><strong>StringHandler.cs</strong></p>
  
  <pre><code>namespace Utilities
  {
      public static class StringHandler
      {
          public static string InsertSpaces(this string source)
          {
              string result = string.Empty;
  
              if (!string.IsNullOrWhiteSpace(source))
              {
                  foreach (char letter in source)
                  {
                      if (char.IsUpper(letter))
                      {
                          result = result.Trim();
                          result += " ";
                      }
                      result += letter;
                  }
              }
              return result.Trim();
          }
      }
  }
  </code></pre>