main.dart

void main() {
  asyncInit();
}

Future<void> asyncInit() async {
  await Future.wait([
    for (var i = 0; i < 10; i++) ...[
      asyncParent(),
    ],
  ]);
  print('---------------------');
  await Future.wait([
    for (var i = 0; i < 10; i++) ...[
      syncParent(),
    ],
  ]);
  print('---------------------');
  await asyncParent();
}

Future<String> asyncParent() async {
  final s = Stopwatch()..start();
  final result = await asyncChild();
  s.stop();
  print('asyncParent: ${s.elapsedMilliseconds}');
  return result;
}

Future<String> asyncChild() async {
  final s = Stopwatch()..start();
  const result = 'foo';
  s.stop();
  print('asyncChild: ${s.elapsedMilliseconds}');
  return result;
}

Future<String> syncParent() async {
  final s = Stopwatch()..start();
  final result = syncChild();
  s.stop();
  print('syncParent: ${s.elapsedMilliseconds}');
  return result;
}

String syncChild() {
  final s = Stopwatch()..start();
  const result = 'foo';
  s.stop();
  print('syncChild: ${s.elapsedMilliseconds}');
  return result;
}