title: Passed function as parameter isn't called on subscribe
body: <p>I'm generating a node where I pass function as such:</p>
  <pre><code>this.navigatinoService.generateNode(null, null... , this.navigationService.displayApkStoreMenu,..)
  </code></pre>
  <p>and the generate function looks something like this.</p>
  <pre><code>public generateNode(translationId: string, iconId: string, display: any, disabled, routerLink: string, children: SideNavNode[]): SideNavNode {
      const node: SideNavNode = {
        translationId: translationId,
        iconId: iconId,
        display: this.userService.getUser().subscribe(() =&gt; node.display = display()),
        disabled: disabled,
        routerLink: routerLink,
        children: children
      };
  
      this.SIDENAV_TREE_DATA.push(node);
      return node;
    }
  </code></pre>
  <p>I wan't to be subscribed to the <code>userService.getUser()</code> which will trigger when user changes. And when the user changes I want to trigger the display function again to either return true or false.</p>
  <p>Here is an explample of the the function displayApkStoreMenu:</p>
  <pre><code>displayApkStoreMenu(): boolean {
      // some code...
      return // either true or false
    }
  </code></pre>
  <p>Right now when the user changes the function isn't called at all and neither does the value of display changes. But I know the subscribe is triggering because when I put <code>console.log</code> instead of <code>node.display = display()</code> it will trigger the <code>console.log</code>.</p>