title: Angular2 Observable isn't triggered by async pipe
body: <p>Consider this simple snippet of angular2/rxjs/typescript</p>
  
  <pre><code>  public rooms: Observable&lt;Room[]&gt;;      
  
    constructor ( ... ) {
  
      this.rooms = this.inspectShipSubject
        .do(() =&gt; console.log('foo'))
        .switchMap(ship =&gt; this.roomByShipService.getRoomsByShip(ship));
  
      //this.rooms.subscribe(); // &lt;-- [1]
    }
  </code></pre>
  
  <p>Here's the template:</p>
  
  <pre><code>&lt;some-component *ngFor="let room of rooms | async" [room]="room"&gt;&lt;/some-component&gt;
  </code></pre>
  
  <p>It doesn't work ('foo' is not printed and no data shows) unless I uncomment the line indicated <code>[1]</code>. Why doesn't the template trigger the observable to execute automatically?</p>
  
  <p>Is there a better way than to use a blank subscribe?</p>