title: Is there a canonical or good way to define a non-busy-wait Future in Scala that never ends?
body: <p>I need to define a mutable Future used as a UI callback. When created, it shouldn't complete until it is assigned an actual computation, so something like this:</p>
  
  <pre><code>var myCallback: Future[Option[Long]] = Future.dummyWait
  </code></pre>
  
  <p>Of course, I could do the following, but that would be a busy wait:</p>
  
  <pre><code>var myCallback: Future[Option[Long]] = Future{while(true){0;}; Some(0L)}
  </code></pre>
  
  <p>If Future isn't the right abstraction, what is?</p>