title: Make sure a service is instantiated
body: <p><strong>Background</strong></p>
  
  <p>We're building an Angular2 app, and are accumulating a lot of specific services relating to one module. All these services are loosely coupled to a <code>Subject&lt;Type&gt;</code> event system in the app. </p>
  
  <p><strong>Instantiation via the Constructor</strong></p>
  
  <p>Because these services are never directly referenced, and only subscribe to events, we just have to instantiate them somehow. Currently we just inject them into a constructor of another service that is used.</p>
  
  <pre><code>// Services not used, just to make sure they're instantiated
  constructor(
    private appService1: AppService1,     
    private appService2: AppService2,
    private appService3: AppService3,
    ...
  ){ }
  </code></pre>
  
  <p>This seems like a bit of a hack, is there a better way to explicitly state services that need to be instantiated without injecting them through a constructor?</p>