fabrik_result 1.1.0

A lightweight toolkit for functional-style types like Either, built for clarity and real-world use.

fabrik_result

Lightweight, explicit result types for Dart and Flutter — model success, failure, and absence of values without exceptions or nulls.

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What's included

Type	Purpose
Either<L, R>	Success (Right) or failure (Left) with exhaustive handling
Option<T>	Value present (Some) or absent (None)
Unit	Typed replacement for void in generic APIs

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Installation

dependencies:
  fabrik_result: ^1.0.1

flutter pub get

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Quick Start

Either — handle failures explicitly

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

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

Because Either is a sealed class, you can also pattern match on it and the compiler will tell you if you miss a case — no default branch needed:

final message = switch (result) {
  Left(value: final failure) => 'Failed: ${failure.message}',
  Right(value: final user) => 'Welcome, ${user.name}',
};

Return values using the helper functions:

Future<Either<Failure, User>> getUser(String id) async {
  try {
    final user = await api.fetchUser(id);
    return right(user);
  } catch (e) {
    return left(Failure(e.toString()));
  }
}

Capture exceptions at the boundary

tryCatch and tryCatchAsync replace that hand-written try/catch:

Future<Either<Failure, User>> getUser(String id) {
  return Either.tryCatchAsync(
    () => api.fetchUser(id),
    (error, stackTrace) => Failure('$error'),
  );
}

Transform and chain

Use map to change the success value and flatMap to run another fallible step. A Left short-circuits the whole chain, so failures propagate untouched:

final result = await getUser(id)
    .then((r) => r.map((user) => user.profile))
    .then((r) => r.flatMap(validateProfile));

// Read it back with a fallback:
final name = result.getOrElse((failure) => 'Anonymous');

Available on Either: map, mapLeft, flatMap, flatMapAsync, getOrElse, swap.

Option — model absence without null

Option<User> cached = findCachedUser();

cached.fold(
  () => showLoginScreen(),
  (user) => showDashboard(user),
);

Option interoperates with Dart's nullable types in both directions, which makes it useful for loosely typed data such as JSON:

final name = Option.fromNullable(json['name'] as String?)
    .where((n) => n.isNotEmpty)
    .map((n) => n.trim())
    .getOrElse(() => 'Anonymous');

// And back to a nullable when an API expects one:
final String? raw = cached.map((u) => u.email).toNullable();

Turn a missing value into a typed failure with toEither:

Either<Failure, User> result =
    cached.toEither(() => Failure('no cached user'));

Available on Option: map, flatMap, getOrElse, where, toNullable, toEither, plus the static Option.fromNullable.

Unit — type-safe void

Use Unit when an operation succeeds but has nothing meaningful to return:

Future<Either<Failure, Unit>> saveSettings(Settings s) async {
  try {
    await storage.write(s);
    return right(unit);
  } catch (e) {
    return left(Failure(e.toString()));
  }
}

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Extras

Either also has side-effect helpers for imperative code:

result.onRight((user) => analytics.track('login'));
result.onLeft((failure) => logger.error(failure));

final user = result.rightOrNull;

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Documentation

Full API reference and guides at fabriktool.com

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Contributing

Found a bug or have a suggestion? Open an issue or pull request on GitHub.

Maintainers

• Ashish Bhakhand