title: C# String Interpolation on <appSettings>
body: <p>I am liking the new Interpolation syntax of C#.</p>
  
  <p>I want to store a dynamic string in my .config file under <code>appSettings</code> and apply interpolation on it. The expected value of <code>interpolatedMessage</code> is <code>"Your User Name is SnowWhite"</code></p>
  
  <p>It would be great if this is possible.
  This will help me to keep the key to be configurable to any combination. (e.g. "SnowWhite is your User Name", "User Name - SnowWhite")</p>
  
  <pre><code> &lt;appSettings&gt;
      &lt;add key="userNameKey" value="Your User Name is {userName}" /&gt;
    &lt;/appSettings&gt;
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/KVfxS.png" rel="noreferrer"><img src="https://i.stack.imgur.com/KVfxS.png" alt="enter image description here"></a></p>