title: Cannot pipe on combineLatest
body: <p>I am trying to follow <a href="https://stackblitz.com/edit/facades-with-rxjs-only" rel="nofollow noreferrer">this example</a> but am running into an issue when using <code>combineLatest()</code>:</p>
  
  <blockquote>
    <p><code>Property 'subscribe' does not exist on type 'OperatorFunction&lt;unknown, [unknown, Item[], User[]]&gt;'</code></p>
  </blockquote>
  
  <p><strong>Here is my facade:</strong></p>
  
  <pre class="lang-js prettyprint-override"><code>import { HttpClient } from '@angular/common/http';
  import { Injectable } from '@angular/core';
  import { BehaviorSubject } from 'rxjs';
  import { combineLatest, distinctUntilChanged, map } from 'rxjs/operators';
  
  export interface User {
    test: string;
  }
  
  export interface Item {
    test: string;
  }
  
  interface State {
    items: Item[];
    users: User[];
  }
  
  let _state: State = {
    items: [],
    users: [],
  };
  
  @Injectable()
  export class Facade {
    private store = new BehaviorSubject&lt;State&gt;(_state);
    private state$ = this.store.asObservable();
  
    items$ = this.state$.pipe(map(state =&gt; state.items), distinctUntilChanged());
    emails$ = this.state$.pipe(map(state =&gt; state.users), distinctUntilChanged());
  
    constructor(private http: HttpClient) {
      combineLatest(this.items$, this.emails$).subscribe(
        ([items, users]) =&gt; {}
      );
    }
  }
  </code></pre>
  
  <p><code>items$</code> and <code>emails$</code> are both Observables. This code nearly mirrors the code in the example above, why am I getting this error?</p>