[compass_app] Standardize on Result factories rather than constructors (#2538)

From my review of the recipes PR in
https://github.com/flutter/website/pull/11444#pullrequestreview-2480423811.

compass_app/app/lib/data/repositories/auth/auth_repository_dev.dart

@@ -16,12 +16,12 @@ class AuthRepositoryDev extends AuthRepository {
     required String email,
     required String password,
   }) async {
-    return Result.ok(null);
+    return const Result.ok(null);
   }
 
   /// Logout is always successful in dev scenarios
   @override
   Future<Result<void>> logout() async {
-    return Result.ok(null);
+    return const Result.ok(null);
   }
 }

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

@@ -31,7 +31,7 @@ class BookingRepositoryLocal implements BookingRepository {
     // Bookings created come without id, we need to assign one
     final bookingWithId = booking.copyWith(id: _sequentialId++);
     _bookings.add(bookingWithId);
-    return Result.ok(null);
+    return const Result.ok(null);
   }
 
   @override
@@ -92,6 +92,6 @@ class BookingRepositoryLocal implements BookingRepository {
   @override
   Future<Result<void>> delete(int id) async {
     _bookings.removeWhere((booking) => booking.id == id);
-    return Result.ok(null);
+    return const Result.ok(null);
   }
 }

compass_app/app/lib/data/repositories/itinerary_config/itinerary_config_repository_memory.dart

@@ -22,6 +22,6 @@ class ItineraryConfigRepositoryMemory implements ItineraryConfigRepository {
     ItineraryConfig itineraryConfig,
   ) async {
     _itineraryConfig = itineraryConfig;
-    return Result.ok(true);
+    return const Result.ok(true);
   }
 }

compass_app/app/lib/data/services/api/api_client.dart

@@ -53,7 +53,7 @@ class ApiClient {
         return Result.ok(
             json.map((element) => Continent.fromJson(element)).toList());
       } else {
-        return Result.error(const HttpException("Invalid response"));
+        return const Result.error(HttpException("Invalid response"));
       }
     } on Exception catch (error) {
       return Result.error(error);
@@ -74,7 +74,7 @@ class ApiClient {
         return Result.ok(
             json.map((element) => Destination.fromJson(element)).toList());
       } else {
-        return Result.error(const HttpException("Invalid response"));
+        return const Result.error(HttpException("Invalid response"));
       }
     } on Exception catch (error) {
       return Result.error(error);
@@ -97,7 +97,7 @@ class ApiClient {
             json.map((element) => Activity.fromJson(element)).toList();
         return Result.ok(activities);
       } else {
-        return Result.error(const HttpException("Invalid response"));
+        return const Result.error(HttpException("Invalid response"));
       }
     } on Exception catch (error) {
       return Result.error(error);
@@ -119,7 +119,7 @@ class ApiClient {
             json.map((element) => BookingApiModel.fromJson(element)).toList();
         return Result.ok(bookings);
       } else {
-        return Result.error(const HttpException("Invalid response"));
+        return const Result.error(HttpException("Invalid response"));
       }
     } on Exception catch (error) {
       return Result.error(error);
@@ -139,7 +139,7 @@ class ApiClient {
         final booking = BookingApiModel.fromJson(jsonDecode(stringData));
         return Result.ok(booking);
       } else {
-        return Result.error(const HttpException("Invalid response"));
+        return const Result.error(HttpException("Invalid response"));
       }
     } on Exception catch (error) {
       return Result.error(error);
@@ -160,7 +160,7 @@ class ApiClient {
         final booking = BookingApiModel.fromJson(jsonDecode(stringData));
         return Result.ok(booking);
       } else {
-        return Result.error(const HttpException("Invalid response"));
+        return const Result.error(HttpException("Invalid response"));
       }
     } on Exception catch (error) {
       return Result.error(error);
@@ -180,7 +180,7 @@ class ApiClient {
         final user = UserApiModel.fromJson(jsonDecode(stringData));
         return Result.ok(user);
       } else {
-        return Result.error(const HttpException("Invalid response"));
+        return const Result.error(HttpException("Invalid response"));
       }
     } on Exception catch (error) {
       return Result.error(error);
@@ -197,9 +197,9 @@ class ApiClient {
       final response = await request.close();
       // Response 204 "No Content", delete was successful
       if (response.statusCode == 204) {
-        return Result.ok(null);
+        return const Result.ok(null);
       } else {
-        return Result.error(const HttpException("Invalid response"));
+        return const Result.error(HttpException("Invalid response"));
       }
     } on Exception catch (error) {
       return Result.error(error);

compass_app/app/lib/data/services/api/auth_api_client.dart

@@ -32,7 +32,7 @@ class AuthApiClient {
         final stringData = await response.transform(utf8.decoder).join();
         return Result.ok(LoginResponse.fromJson(jsonDecode(stringData)));
       } else {
-        return Result.error(const HttpException("Login error"));
+        return const Result.error(HttpException("Login error"));
       }
     } on Exception catch (error) {
       return Result.error(error);

compass_app/app/lib/data/services/shared_preferences_service.dart

@@ -32,7 +32,7 @@ class SharedPreferencesService {
         _log.finer('Replaced token');
         await sharedPreferences.setString(_tokenKey, token);
       }
-      return Result.ok(null);
+      return const Result.ok(null);
     } on Exception catch (e) {
       _log.warning('Failed to set token', e);
       return Result.error(e);

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

@@ -98,7 +98,7 @@ class BookingCreateUseCase {
       case Ok<List<Destination>>():
         final destination = result.value
             .firstWhere((destination) => destination.ref == destinationRef);
-        return Ok(destination);
+        return Result.ok(destination);
       case Error<List<Destination>>():
         return Result.error(result.error);
     }

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

@@ -37,7 +37,7 @@ class BookingShareUseCase {
     try {
       await _share(text);
       _log.fine('Shared booking');
-      return Result.ok(null);
+      return const Result.ok(null);
     } on Exception catch (error) {
       _log.severe('Failed to share booking', error);
       return Result.error(error);

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

@@ -61,7 +61,7 @@ class BookingViewModel extends ChangeNotifier {
             _log.fine('Created Booking');
             _booking = result.value;
             notifyListeners();
-            return Result.ok(null);
+            return const Result.ok(null);
           case Error<Booking>():
             _log.warning('Booking error: ${result.error}');
             notifyListeners();

compass_app/app/lib/utils/result.dart

@@ -18,11 +18,11 @@
 sealed class Result<T> {
   const Result();
 
-  /// Creates an instance of Result containing a value
+  /// Creates a successful [Result], completed with the specified [value].
-  factory Result.ok(T value) => Ok(value);
+  const factory Result.ok(T value) = Ok._;
 
-  /// Create an instance of Result containing an error
+  /// Creates an error [Result], completed with the specified [error].
-  factory Result.error(Exception error) => Error(error);
+  const factory Result.error(Exception error) = Error._;
 
   /// Convenience method to cast to Ok
   Ok<T> get asOk => this as Ok<T>;
@@ -33,7 +33,7 @@ sealed class Result<T> {
 
 /// Subclass of Result for values
 final class Ok<T> extends Result<T> {
-  const Ok(this.value);
+  const Ok._(this.value);
 
   /// Returned value in result
   final T value;
@@ -44,7 +44,7 @@ final class Ok<T> extends Result<T> {
 
 /// Subclass of Result for errors
 final class Error<T> extends Result<T> {
-  const Error(this.error);
+  const Error._(this.error);
 
   /// Returned error in result
   final Exception error;

compass_app/app/testing/fakes/services/fake_auth_api_client.dart

@@ -11,7 +11,7 @@ class FakeAuthApiClient implements AuthApiClient {
   @override
   Future<Result<LoginResponse>> login(LoginRequest loginRequest) async {
     if (loginRequest.email == 'EMAIL' && loginRequest.password == 'PASSWORD') {
-      return Result.ok(const LoginResponse(token: 'TOKEN', userId: '123'));
+      return const Result.ok(LoginResponse(token: 'TOKEN', userId: '123'));
     }
     return Result.error(Exception('ERROR!'));
   }