Completer

main.dart

import 'dart:async';

Future<dynamic> someFutureResult(){
   final Completer c = Completer();
   // complete will be called in 3 seconds by the timer.
   new Timer(Duration(seconds: 3), () => c.complete("you should see me second"));
   return c.future;
}

main(){
   someFutureResult().then((result) => print('$result'));
   print("you should see me first");
}