completer_example.dart

import 'dart:async';

void main() async {
  print('a');
  await waitTime(Duration(seconds: 3));
  print('b');
}

Future waitTime(Duration duration) {
  Completer completer = Completer();
  print('created completer');
  Future.delayed(duration, () => completer.complete());
  return completer.future;
}