title: Angular 2 template var not updating in ngSwitch
body: <p>I have a variable threadCount which gets set via user input and showing the value on the same page.</p>
  
  <p>It works fine for normal interpolation</p>
  
  <pre><code>&lt;p&gt;Threads: {{threadCount}}&lt;/p&gt;
  </code></pre>
  
  <p>But right below that I am wanting to append it to certain threads (if the name ends in '-').</p>
  
  <p>The following works if I threadCount is defined before the thread is added to selectedThreads</p>
  
  <pre><code>  &lt;p&gt;Threads: {{threadCount}}&lt;/p&gt;
    &lt;p&gt;Selected LFKs:
      &lt;span *ngFor="let lfk of selectedLFKs; let isLast=last; "&gt;
        &lt;span [ngSwitch]="lfk"&gt;
          &lt;span *ngSwitchCase="lfk.charAt(lfk.length -1) === '-'"&gt;{{lfk}}{{threadCount}}{{isLast ? '': ', '}}&lt;/span&gt;
          &lt;span *ngSwitchDefault&gt;{{lfk}}{{isLast ? '': ', '}}&lt;/span&gt;
        &lt;/span&gt;
      &lt;/span&gt;
    &lt;/p&gt;
  </code></pre>
  
  <p>Once the user changes threadCount, the first threadCount interpolation is updated but the one inside of the ngFor and ngSwitch does not.</p>
  
  <ol>
  <li>What is the proper way to do this?</li>
  <li>What is the easiest way to do this?</li>
  </ol>