title: Keeping final fields on the Widget or the State?
body: <p>Where should one keep final values?</p>
  
  <p>In the <code>StatefulWidget</code> (my subclass of course) instance and access it from the <code>State</code> (subclass) via <code>widget.thatFinalField</code>, or</p>
  
  <p>In the <code>State</code> itself. I've seen both approaches already.. Any pros and cons for each of them?</p>