title: Creating Dynamic Classes in Jade/Pug
body: <p>I'm trying to add a dynamic class to a jade template. Like so:</p>
  
  <pre><code>- var obj = {a: 1, b: 2, c: 3};
  - var len = Object.keys(obj).length;
  
  .abc-#{len}
  </code></pre>
  
  <p>But the compiler is taking exception to this:</p>
  
  <pre><code>  &gt; 4| .abc-#{len}
  ------------^
  
  Unexpected token `interpolation` expected `text`, `interpolated-code`, `code`, `:`, `slash`, `newline` or `eos`
  </code></pre>
  
  <p>I've tried everything I could think of. Been scouring <a href="https://pugjs.org/language/interpolation.html" rel="noreferrer">https://pugjs.org/language/interpolation.html</a>. Could really use a hand.</p>
  
  <p>Thanks.</p>