title: Set an HTML class to host in an Angular directive
body: <p>How would you do to add and set an HTML class that can be changed with a parameter, with an Angular directive  ?
  Let's say we have a div with an already existing class, but no directive :</p>
  <pre><code>&lt;div class=&quot;myClass&quot;&gt;&lt;/div&gt;
  </code></pre>
  <p>Now, we want to attach a directive to it, and one parameter :</p>
  <pre><code>&lt;div directiveName set=&quot;X&quot; class=&quot;myClass myClass-X&quot;&gt;&lt;/div&gt;
  </code></pre>
  <p>If I need a 4, then my class added dynamically would be changed like that :</p>
  <pre><code>&lt;div directiveName set=&quot;4&quot; class=&quot;myClass myClass-4&quot;&gt;&lt;/div&gt;
  </code></pre>
  <p>I totally know how to add a class with @hostbinding, but I can't find how to change this one dynamically with my &quot;set&quot; parameter</p>
  <p>Thank you very much</p>