title: Dart StreamController with two arguments
body: <p>I am currently developing on Flutter, using the BLoC pattern, and I would like to accept another parameter (or argument) in my <code>StreamController</code>. I could have used a Map or a class but is there a way to do it using Dart types?</p>
  
  <p>Is something similar to <code>StreamController&lt;int, String&gt;</code> possible?</p>