fabrik_result

fabrik_result is a minimal result-handling toolkit for Dart and Flutter. It gives you a typed way to model success and failure without relying on exceptions — making your domain logic easier to read, test, and reason about.

Installation

dart pub add fabrik_result

Or add it to your pubspec.yaml:

dependencies:
  fabrik_result: ^1.0.1

Import it in your Dart files:

import 'package:fabrik_result/fabrik_result.dart';

---

Either

Either<L, R> is a sealed type that holds either a left value (conventionally failure) or a right value (conventionally success). It makes the possible outcomes of an operation explicit in the return type.

Either<Failure, User> result = await userRepository.getUser(id);

result.fold(
  (failure) => showError(failure.message),
  (user) => navigateToProfile(user),
);

Constructing values:

// Success
return Right(user);

// Failure
return Left(Failure('User not found'));

Checking the side:

result.isRight  // true if success
result.isLeft   // true if failure

---

Unit

Unit is a typed void — use it when an operation succeeds but has nothing meaningful to return.

Either<Failure, Unit> result = await settingsRepository.save(settings);

result.fold(
  (failure) => showError(failure.message),
  (_) => showSuccess('Settings saved'),
);

Instead of returning Either<Failure, void> (which isn’t valid in Dart), return Either<Failure, Unit> and use Right(unit) as the success value.

---

In a Repository

A typical repository method using fabrik_result:

Future<Either<Failure, User>> getUser(String id) async {
  try {
    final model = await dataSource.fetchUser(id);
    return Right(model.toEntity());
  } catch (e) {
    return Left(Failure(e.toString()));
  }
}

---

Why Not Try-Catch?

	try-catch	Either
Failure is explicit in signature	No	Yes
Caller must handle failure	No	Yes
Testable without exceptions	Hard	Easy
Composable	No	Yes

fabrik_result is a lightweight alternative to packages like dartz — it provides only Either and Unit, nothing more.