title: How to assign result of async pipe to variable without *ngIf in Angular 6
body: <p>Is it possible to assign (areShipsExpanded$ | async) to variable without *ngIf? Because in case that this is flag <code>true</code>/<code>false</code> when I have: <code>*ngIf="(areShipsExpanded$ | async) as flag"</code> then button is not displaying in case of false. </p>
  
  <p>And I would like something like this:</p>
  
  <pre><code>&lt;button *let="(areShipsExpanded$ | async) as flag"
     (click)="expandAllShips(flag)"&gt;{{(flag ? "Collapse" : "Expand"}}
  &lt;/button&gt;
  </code></pre>