(Dart) FutureOr handling differences

readme.md

(Dart) FutureOr handling differences

Created with <3 with dartpad.dev.

main.dart

import 'dart:async';

/// Produces the following output (since [futureOrResult] value is available synchronously):
/// ```
/// process: 0
/// result: 0
/// process: 1
/// ```
Future<void> main() async {
  unawaited(process());
  final futureOrResult = x();
  if (futureOrResult is Future) {
    final result = await futureOrResult;
    print('result: $result');
  } else {
    print('result: $futureOrResult');
  }
}

/// Rename this to `main` to see a difference in behavior.
///
/// Produces the following output (since [futureOrResult] value is available only asynchronously):
/// ```
/// process: 0
/// process: 1
/// result: 0
/// ```
Future<void> _main() async {
  unawaited(process());
  final result = await x();
  print('result: $result');
}

Future<void> process() async {
  print('process: 0');
  await Future.value();
  print('process: 1');
}

FutureOr<int> x() {
  return 0;
}