main.dart

import 'package:flutter/foundation.dart';

void main() {
  print('start');
  awaitFn();
  thenFn();
  print('end');
}

Future<void> awaitFn() async {
  print('awaitFn start');
  await SynchronousFuture(42);
  print('awaitFn end');
}

Future<void> thenFn() {
  print('thenFn start');
  return SynchronousFuture(42).then((value) {
    print('thenFn end');
  });
}