Testing behavior of switch and async

switch_async.dart

// Stubs for package:http.
enum HttpMethod {
  GET,
  POST,
  PATCH,
}

class HttpStatus {
  static const int ok = 200;
  static const int methodNotAllowed = 405;
}

Future<Response> doGetAsync() async {
  return Response(statusCode: HttpStatus.ok);
}

Future<Response> doPostAsync() async {
  return Response(statusCode: HttpStatus.ok);
}

class Response {
  final int statusCode;

  Response({required this.statusCode});
}

// Original code before refacotoring to switch.
// Note how some paths return a future, some return a value
// (which dart implicitly wraps as a future).
Future<Response> respondIf(HttpMethod method) async {
  if (method == HttpMethod.GET) {
    return doGetAsync();
  }
  if (method == HttpMethod.POST) {
    return doPostAsync();
  }
  return Response(statusCode: HttpStatus.methodNotAllowed);
}

// Refactor to use switch.
// This broke in our larger codebase...
Future<Response> respondSwitch(HttpMethod method) async {
  return switch (method) {
    HttpMethod.GET => doGetAsync(),
    HttpMethod.POST => doPostAsync(),
    // Don't I have to wrap it in a Future.value?!?
    _ => Response(statusCode: HttpStatus.methodNotAllowed)
  };
}

// How we had to do this in our larger codebase otherwise
// analyzer complained:
// "A value of type 'Object' cannot be returned from the
// function 'onRequest' because it has a return type of of
// Future<Response>.
Future<Response> respondSwitchFuture(HttpMethod method) async {
  return switch (method) {
    HttpMethod.GET => doGetAsync(),
    HttpMethod.POST => doPostAsync(),
    _ => Future.value(Response(statusCode: HttpStatus.methodNotAllowed))
  };
}

// Another way we could have done it.
Future<Response> respondSwitchAwait(HttpMethod method) async {
  return switch (method) {
    HttpMethod.GET => await doGetAsync(),
    HttpMethod.POST => await doPostAsync(),
    _ => Response(statusCode: HttpStatus.methodNotAllowed)
  };
}

void main() async {
  await respondIf(HttpMethod.GET);
  await respondSwitch(HttpMethod.GET);
  await respondSwitchFuture(HttpMethod.GET);
  await respondSwitchAwait(HttpMethod.GET);
}