refactor Result class, remove asOk and asError (#2542)

As discussed in the PR for the Result pattern implementation
(https://github.com/flutter/website/pull/11444) @parlough recommended
that `asError` and `asOk` should be not be used, and instead we should
use proper exhaustiveness checking.

This PR removes the two "convenience" methods and refactors code.

In some cases, it was enough with writing a proper `if` clause, while in
others it was necessary to use a `switch`.

Still, they are present in the `testing` folder, as they can be useful
for testing purposes.

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I have added sample code updates to the [changelog].
- [x] I updated/added relevant documentation (doc comments with `///`).

If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Style-guide-for-Flutter-repo.md
[CLA]: https://cla.developers.google.com/
[Discord]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Chat.md
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md
[changelog]: ../CHANGELOG.md

compass_app/app/lib/data/repositories/activity/activity_repository_remote.dart

@@ -24,8 +24,8 @@ class ActivityRepositoryRemote implements ActivityRepository {
     if (!_cachedData.containsKey(ref)) {
       // No cached data, request activities
       final result = await _apiClient.getActivityByDestination(ref);
-      if (result is Ok) {
-        _cachedData[ref] = result.asOk.value;
+      if (result is Ok<List<Activity>>) {
+        _cachedData[ref] = result.value;
       }
       return result;
     } else {

compass_app/app/lib/data/repositories/booking/booking_repository_remote.dart

@@ -42,18 +42,22 @@ class BookingRepositoryRemote implements BookingRepository {
     try {
       // Get booking by ID from server
       final resultBooking = await _apiClient.getBooking(id);
-      if (resultBooking is Error<BookingApiModel>) {
-        return Result.error(resultBooking.error);
+      switch (resultBooking) {
+        case Error<BookingApiModel>():
+          return Result.error(resultBooking.error);
+        case Ok<BookingApiModel>():
       }
-      final booking = resultBooking.asOk.value;
+      final booking = resultBooking.value;
 
       // Load destinations if not loaded yet
       if (_cachedDestinations == null) {
         final resultDestination = await _apiClient.getDestinations();
-        if (resultDestination is Error<List<Destination>>) {
-          return Result.error(resultDestination.error);
+        switch (resultDestination) {
+          case Error<List<Destination>>():
+            return Result.error(resultDestination.error);
+          case Ok<List<Destination>>():
         }
-        _cachedDestinations = resultDestination.asOk.value;
+        _cachedDestinations = resultDestination.value;
       }
 
       // Get destination for booking
@@ -62,11 +66,12 @@ class BookingRepositoryRemote implements BookingRepository {
 
       final resultActivities =
           await _apiClient.getActivityByDestination(destination.ref);
-
-      if (resultActivities is Error<List<Activity>>) {
-        return Result.error(resultActivities.error);
+      switch (resultActivities) {
+        case Error<List<Activity>>():
+          return Result.error(resultActivities.error);
+        case Ok<List<Activity>>():
       }
-      final activities = resultActivities.asOk.value
+      final activities = resultActivities.value
           .where((activity) => booking.activitiesRef.contains(activity.ref))
           .toList();
 
@@ -88,20 +93,22 @@ class BookingRepositoryRemote implements BookingRepository {
   Future<Result<List<BookingSummary>>> getBookingsList() async {
     try {
       final result = await _apiClient.getBookings();
-      if (result is Error<List<BookingApiModel>>) {
-        return Result.error(result.error);
+      switch (result) {
+        case Ok<List<BookingApiModel>>():
+          final bookingsApi = result.value;
+          return Result.ok(bookingsApi
+              .map(
+                (bookingApi) => BookingSummary(
+                  id: bookingApi.id!,
+                  name: bookingApi.name,
+                  startDate: bookingApi.startDate,
+                  endDate: bookingApi.endDate,
+                ),
+              )
+              .toList());
+        case Error<List<BookingApiModel>>():
+          return Result.error(result.error);
       }
-      final bookingsApi = result.asOk.value;
-      return Result.ok(bookingsApi
-          .map(
-            (bookingApi) => BookingSummary(
-              id: bookingApi.id!,
-              name: bookingApi.name,
-              startDate: bookingApi.startDate,
-              endDate: bookingApi.endDate,
-            ),
-          )
-          .toList());
     } on Exception catch (e) {
       return Result.error(e);
     }

compass_app/app/lib/data/repositories/continent/continent_repository_remote.dart

@@ -24,9 +24,9 @@ class ContinentRepositoryRemote implements ContinentRepository {
     if (_cachedData == null) {
       // No cached data, request continents
       final result = await _apiClient.getContinents();
-      if (result is Ok) {
+      if (result is Ok<List<Continent>>) {
         // Store value if result Ok
-        _cachedData = result.asOk.value;
+        _cachedData = result.value;
       }
       return result;
     } else {

compass_app/app/lib/data/repositories/destination/destination_repository_remote.dart

@@ -24,9 +24,9 @@ class DestinationRepositoryRemote implements DestinationRepository {
     if (_cachedData == null) {
       // No cached data, request destinations
       final result = await _apiClient.getDestinations();
-      if (result is Ok) {
+      if (result is Ok<List<Destination>>) {
         // Store value if result Ok
-        _cachedData = result.asOk.value;
+        _cachedData = result.value;
       }
       return result;
     } else {

compass_app/app/lib/domain/use_cases/booking/booking_create_use_case.dart

@@ -40,11 +40,13 @@ class BookingCreateUseCase {
     }
     final destinationResult =
         await _fetchDestination(itineraryConfig.destination!);
-    if (destinationResult is Error<Destination>) {
-      _log.warning('Error fetching destination: ${destinationResult.error}');
-      return Result.error(destinationResult.error);
+    switch (destinationResult) {
+      case Ok<Destination>():
+        _log.fine('Destination loaded: ${destinationResult.value.ref}');
+      case Error<Destination>():
+        _log.warning('Error fetching destination: ${destinationResult.error}');
+        return Result.error(destinationResult.error);
     }
-    _log.fine('Destination loaded: ${destinationResult.asOk.value.ref}');
 
     // Get Activity objects from repository
     if (itineraryConfig.activities.isEmpty) {
@@ -54,11 +56,13 @@ class BookingCreateUseCase {
     final activitiesResult = await _activityRepository.getByDestination(
       itineraryConfig.destination!,
     );
-    if (activitiesResult is Error<List<Activity>>) {
-      _log.warning('Error fetching activities: ${activitiesResult.error}');
-      return Result.error(activitiesResult.error);
+    switch (activitiesResult) {
+      case Error<List<Activity>>():
+        _log.warning('Error fetching activities: ${activitiesResult.error}');
+        return Result.error(activitiesResult.error);
+      case Ok<List<Activity>>():
     }
-    final activities = activitiesResult.asOk.value
+    final activities = activitiesResult.value
         .where(
           (activity) => itineraryConfig.activities.contains(activity.ref),
         )
@@ -74,7 +78,7 @@ class BookingCreateUseCase {
     final booking = Booking(
       startDate: itineraryConfig.startDate!,
       endDate: itineraryConfig.endDate!,
-      destination: destinationResult.asOk.value,
+      destination: destinationResult.value,
       activity: activities,
     );
 

compass_app/app/lib/ui/activities/view_models/activities_viewmodel.dart

@@ -8,6 +8,7 @@ import 'package:logging/logging.dart';
 import '../../../data/repositories/activity/activity_repository.dart';
 import '../../../data/repositories/itinerary_config/itinerary_config_repository.dart';
 import '../../../domain/models/activity/activity.dart';
+import '../../../domain/models/itinerary_config/itinerary_config.dart';
 import '../../../utils/command.dart';
 import '../../../utils/result.dart';
 
@@ -45,21 +46,23 @@ class ActivitiesViewModel extends ChangeNotifier {
 
   Future<Result<void>> _loadActivities() async {
     final result = await _itineraryConfigRepository.getItineraryConfig();
-    if (result is Error) {
-      _log.warning(
-        'Failed to load stored ItineraryConfig',
-        result.asError.error,
-      );
-      return result;
+    switch (result) {
+      case Error<ItineraryConfig>():
+        _log.warning(
+          'Failed to load stored ItineraryConfig',
+          result.error,
+        );
+        return result;
+      case Ok<ItineraryConfig>():
     }
 
-    final destinationRef = result.asOk.value.destination;
+    final destinationRef = result.value.destination;
     if (destinationRef == null) {
       _log.severe('Destination missing in ItineraryConfig');
       return Result.error(Exception('Destination not found'));
     }
 
-    _selectedActivities.addAll(result.asOk.value.activities);
+    _selectedActivities.addAll(result.value.activities);
 
     final resultActivities =
         await _activityRepository.getByDestination(destinationRef);
@@ -120,21 +123,23 @@ class ActivitiesViewModel extends ChangeNotifier {
 
   Future<Result<void>> _saveActivities() async {
     final resultConfig = await _itineraryConfigRepository.getItineraryConfig();
-    if (resultConfig is Error) {
-      _log.warning(
-        'Failed to load stored ItineraryConfig',
-        resultConfig.asError.error,
-      );
-      return resultConfig;
+    switch (resultConfig) {
+      case Error<ItineraryConfig>():
+        _log.warning(
+          'Failed to load stored ItineraryConfig',
+          resultConfig.error,
+        );
+        return resultConfig;
+      case Ok<ItineraryConfig>():
     }
 
-    final itineraryConfig = resultConfig.asOk.value;
+    final itineraryConfig = resultConfig.value;
     final result = await _itineraryConfigRepository.setItineraryConfig(
         itineraryConfig.copyWith(activities: _selectedActivities.toList()));
     if (result is Error) {
       _log.warning(
         'Failed to store ItineraryConfig',
-        result.asError.error,
+        result.error,
       );
     }
     return result;

compass_app/app/lib/ui/booking/view_models/booking_viewmodel.dart

@@ -65,7 +65,7 @@ class BookingViewModel extends ChangeNotifier {
           case Error<Booking>():
             _log.warning('Booking error: ${result.error}');
             notifyListeners();
-            return Result.error(result.asError.error);
+            return Result.error(result.error);
         }
       case Error<ItineraryConfig>():
         _log.warning('ItineraryConfig error: ${itineraryConfig.error}');

compass_app/app/lib/ui/results/view_models/results_viewmodel.dart

@@ -50,14 +50,16 @@ class ResultsViewModel extends ChangeNotifier {
   Future<Result<void>> _search() async {
     // Load current itinerary config
     final resultConfig = await _itineraryConfigRepository.getItineraryConfig();
-    if (resultConfig is Error) {
-      _log.warning(
-        'Failed to load stored ItineraryConfig',
-        resultConfig.asError.error,
-      );
-      return resultConfig;
+    switch (resultConfig) {
+      case Error<ItineraryConfig>():
+        _log.warning(
+          'Failed to load stored ItineraryConfig',
+          resultConfig.error,
+        );
+        return resultConfig;
+      case Ok<ItineraryConfig>():
     }
-    _itineraryConfig = resultConfig.asOk.value;
+    _itineraryConfig = resultConfig.value;
     notifyListeners();
 
     final result = await _destinationRepository.getDestinations();
@@ -86,15 +88,17 @@ class ResultsViewModel extends ChangeNotifier {
     assert(destinationRef.isNotEmpty, "destinationRef should not be empty");
 
     final resultConfig = await _itineraryConfigRepository.getItineraryConfig();
-    if (resultConfig is Error) {
-      _log.warning(
-        'Failed to load stored ItineraryConfig',
-        resultConfig.asError.error,
-      );
-      return resultConfig;
+    switch (resultConfig) {
+      case Error<ItineraryConfig>():
+        _log.warning(
+          'Failed to load stored ItineraryConfig',
+          resultConfig.error,
+        );
+        return resultConfig;
+      case Ok<ItineraryConfig>():
     }
 
-    final itineraryConfig = resultConfig.asOk.value;
+    final itineraryConfig = resultConfig.value;
     final result = await _itineraryConfigRepository
         .setItineraryConfig(itineraryConfig.copyWith(
       destination: destinationRef,
@@ -103,7 +107,7 @@ class ResultsViewModel extends ChangeNotifier {
     if (result is Error) {
       _log.warning(
         'Failed to store ItineraryConfig',
-        result.asError.error,
+        result.error,
       );
     }
     return result;

compass_app/app/lib/ui/search_form/view_models/search_form_viewmodel.dart

@@ -99,14 +99,10 @@ class SearchFormViewModel extends ChangeNotifier {
     final result = await _continentRepository.getContinents();
     switch (result) {
       case Ok():
-        {
-          _continents = result.value;
-          _log.fine('Continents (${_continents.length}) loaded');
-        }
+        _continents = result.value;
+        _log.fine('Continents (${_continents.length}) loaded');
       case Error():
-        {
-          _log.warning('Failed to load continents', result.asError.error);
-        }
+        _log.warning('Failed to load continents', result.error);
     }
     notifyListeners();
     return result;
@@ -116,27 +112,23 @@ class SearchFormViewModel extends ChangeNotifier {
     final result = await _itineraryConfigRepository.getItineraryConfig();
     switch (result) {
       case Ok<ItineraryConfig>():
-        {
-          final itineraryConfig = result.value;
-          _selectedContinent = itineraryConfig.continent;
-          if (itineraryConfig.startDate != null &&
-              itineraryConfig.endDate != null) {
-            _dateRange = DateTimeRange(
-              start: itineraryConfig.startDate!,
-              end: itineraryConfig.endDate!,
-            );
-          }
-          _guests = itineraryConfig.guests ?? 0;
-          _log.fine('ItineraryConfig loaded');
-          notifyListeners();
-        }
-      case Error<ItineraryConfig>():
-        {
-          _log.warning(
-            'Failed to load stored ItineraryConfig',
-            result.asError.error,
+        final itineraryConfig = result.value;
+        _selectedContinent = itineraryConfig.continent;
+        if (itineraryConfig.startDate != null &&
+            itineraryConfig.endDate != null) {
+          _dateRange = DateTimeRange(
+            start: itineraryConfig.startDate!,
+            end: itineraryConfig.endDate!,
           );
         }
+        _guests = itineraryConfig.guests ?? 0;
+        _log.fine('ItineraryConfig loaded');
+        notifyListeners();
+      case Error<ItineraryConfig>():
+        _log.warning(
+          'Failed to load stored ItineraryConfig',
+          result.error,
+        );
     }
     return result;
   }

compass_app/app/lib/utils/result.dart

@@ -23,12 +23,6 @@ sealed class Result<T> {
 
   /// Creates an error [Result], completed with the specified [error].
   const factory Result.error(Exception error) = Error._;
-
-  /// Convenience method to cast to Ok
-  Ok<T> get asOk => this as Ok<T>;
-
-  /// Convenience method to cast to Error
-  Error get asError => this as Error<T>;
 }
 
 /// Subclass of Result for values

compass_app/app/test/data/repositories/activity/activity_repository_local_test.dart

@@ -7,6 +7,8 @@ import 'package:compass_app/data/services/local/local_data_service.dart';
 import 'package:compass_app/utils/result.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import '../../../../testing/utils/result.dart';
+
 void main() {
   group('ActivityRepositoryLocal tests', () {
     // To load assets

compass_app/app/test/data/repositories/activity/activity_repository_remote_test.dart

@@ -8,6 +8,7 @@ import 'package:compass_app/utils/result.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../../../../testing/fakes/services/fake_api_client.dart';
+import '../../../../testing/utils/result.dart';
 
 void main() {
   group('ActivityRepositoryRemote tests', () {

compass_app/app/test/data/repositories/booking/booking_repository_remote_test.dart

@@ -9,6 +9,7 @@ import 'package:flutter_test/flutter_test.dart';
 
 import '../../../../testing/fakes/services/fake_api_client.dart';
 import '../../../../testing/models/booking.dart';
+import '../../../../testing/utils/result.dart';
 
 void main() {
   group('BookingRepositoryRemote tests', () {

compass_app/app/test/data/repositories/continent/continent_repository_remote_test.dart

@@ -8,6 +8,7 @@ import 'package:compass_app/utils/result.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../../../../testing/fakes/services/fake_api_client.dart';
+import '../../../../testing/utils/result.dart';
 
 void main() {
   group('ContinentRepositoryRemote tests', () {

compass_app/app/test/data/repositories/destination/destination_repository_local_test.dart

@@ -7,6 +7,8 @@ import 'package:compass_app/utils/result.dart';
 import 'package:compass_app/data/repositories/destination/destination_repository_local.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import '../../../../testing/utils/result.dart';
+
 void main() {
   group('DestinationRepositoryLocal tests', () {
     // To load assets

compass_app/app/test/data/repositories/destination/destination_repository_remote_test.dart

@@ -8,6 +8,7 @@ import 'package:compass_app/utils/result.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../../../../testing/fakes/services/fake_api_client.dart';
+import '../../../../testing/utils/result.dart';
 
 void main() {
   group('DestinationRepositoryRemote tests', () {

compass_app/app/test/data/services/api/api_client_test.dart

@@ -12,6 +12,7 @@ import '../../../../testing/models/activity.dart';
 import '../../../../testing/models/booking.dart';
 import '../../../../testing/models/destination.dart';
 import '../../../../testing/models/user.dart';
+import '../../../../testing/utils/result.dart';
 
 void main() {
   group('ApiClient', () {

compass_app/app/test/data/services/api/auth_api_client_test.dart

@@ -8,6 +8,7 @@ import 'package:compass_app/data/services/api/model/login_response/login_respons
 import 'package:flutter_test/flutter_test.dart';
 
 import '../../../../testing/mocks.dart';
+import '../../../../testing/utils/result.dart';
 
 void main() {
   group('AuthApiClient', () {

compass_app/app/test/domain/use_cases/booking/booking_create_use_case_test.dart

@@ -12,6 +12,7 @@ import '../../../../testing/fakes/repositories/fake_destination_repository.dart'
 import '../../../../testing/models/activity.dart';
 import '../../../../testing/models/booking.dart';
 import '../../../../testing/models/destination.dart';
+import '../../../../testing/utils/result.dart';
 
 void main() {
   group('BookingCreateUseCase tests', () {

compass_app/app/test/utils/command_test.dart

@@ -6,6 +6,8 @@ import 'package:compass_app/utils/command.dart';
 import 'package:compass_app/utils/result.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import '../../testing/utils/result.dart';
+
 void main() {
   group('Command0 tests', () {
     test('should complete void command', () async {
@@ -89,7 +91,7 @@ void main() {
     test('should complete bool command, bool argument', () async {
       // Action that returns bool argument
       final command =
-          Command1<bool, bool>((a) => Future.value(Result.ok(true)));
+          Command1<bool, bool>((a) => Future.value(const Result.ok(true)));
 
       // Run action with result and argument
       await command.execute(true);

compass_app/app/testing/utils/result.dart

@@ -0,0 +1,9 @@
+import 'package:compass_app/utils/result.dart';
+
+extension ResultCast<T> on Result<T> {
+  /// Convenience method to cast to Ok
+  Ok<T> get asOk => this as Ok<T>;
+
+  /// Convenience method to cast to Error
+  Error get asError => this as Error<T>;
+}