title: .share() with .subscribe() _isScalar is missing
body: <p>I am trying to use <code>share()</code> with <code>subscribe()</code> but got error message as follow. Initially, i started with subscribe. How can this be fix?</p>
  
  <p>My intention is to execute the logic in subscribe. Share is needed to prevent multiple call with async pipe.</p>
  
  <blockquote>
    <p>Type 'Subscription' is not assignable to type 'Observable'.<br>
    Property '_isScalar' is missing in type 'Subscription'. (property)
    PostDetailPage.post: Observable</p>
  </blockquote>
  
  <pre><code> this.post = this.data.getPostById(this.postId).share().subscribe(data =&gt; {
            this.post = data;
        },
        err =&gt; {
            console.log("Oops!");
        })
  </code></pre>