title: extension method on enum not being called
body: <p>I've done a fair bit of reading and there are plenty of answers to very similar questions but even following those I can't get this to work. The extension method is static, public, has <code>this</code>,  is in the same namespace so should not need importing... what am I missing? My C# isn't great.</p>
  <pre><code>namespace LDB
  {
  
      public enum Neg { isNegated, notNegated };
  
      static class NegStringifier {
          public static string ToString(this Neg n) {
              string res = n switch {
                  Neg.isNegated =&gt; &quot;flowers&quot;,
                  Neg.notNegated =&gt; &quot;kittens&quot;,
                  //_ =&gt; null
              };
              return res;
          }
      }
  
      public class Program
      {
          static void Main(string[] args)
          {
              System.Console.WriteLine(Neg.isNegated.ToString());
              System.Console.WriteLine(Neg.notNegated.ToString());
              ...
  </code></pre>
  <p>output:</p>
  <pre><code>isNegated
  notNegated
  </code></pre>
  <p>Apologies up front, I know this is going to be something trivial but I can't see what.</p>