title: Initializing final fields from a subclass in Dart
body: <p>This does not work:</p>
  
  <pre><code>abstract class Par {
    final int x;
  }
  
  class Sub extends Par {
    Sub(theX) {
      this.x = theX;
    }
  }
  </code></pre>
  
  <p>I get an error in Par saying x must be initialized:</p>
  
  <pre><code>warning: The final variable 'x' must be initialized
  warning: 'x' cannot be used as a setter, it is final
  </code></pre>