flutter_stasis_dartz

dartz adapter for flutter_stasis.

If your use cases return Future<Either<Failure, T>>, this package bridges them to StasisViewModel with zero boilerplate. The core package has no dependency on dartz — this adapter is completely optional.

---

Installation

dependencies:
  flutter_stasis: ^1.0.0
  flutter_stasis_dartz: ^1.0.0
  dartz: ^0.10.1

---

Usage

Import the adapter and call executeEither exactly like execute:

import 'package:flutter_stasis_dartz/flutter_stasis_dartz.dart';

class ProjectsViewModel
    extends StasisViewModel<AppFailure, List<Project>, ProjectsState> {

  ProjectsViewModel(this._getProjects)
      : super(ProjectsState.initial());

  final GetProjectsUseCase _getProjects; // returns Future<Either<AppFailure, List<Project>>>

  // Minimal — onError falls back to setError automatically
  Future<void> load() => executeEither(
    command: _getProjects.call,
    onSuccess: setSuccess,
  );

  // With loading indicator
  Future<void> reload() => executeEither(
    command: _getProjects.call,
    onSuccess: setSuccess,
    onLoading: setLoading,
  );

  // Custom error handling
  Future<void> loadSilently() => executeEither(
    command: _getProjects.call,
    onSuccess: setSuccess,
    onError: (f) => emit(ShowSnackBarEvent(f.message)),
  );
}

onSuccess is required. onError is optional — defaults to setError. onLoading is optional.

executeEither wraps Future<Either<F, R>> into a Command<F, R> internally and delegates to execute.

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With concurrency policy

executeEither accepts the same CommandPolicy as execute:

Future<void> search(String query) => executeEither(
  command: () => _searchUseCase(query),
  onSuccess: setSuccess,
  onLoading: setLoading,
  policy: CommandPolicy.restartable,
);

---

Converting Either manually

If you need to convert an Either result outside of a ViewModel, use the extension:

import 'package:flutter_stasis_dartz/flutter_stasis_dartz.dart';

final either = await someUseCase();
final result = either.toCommandResult(); // CommandResult<F, R>

Or wrap any Either-returning function as a Command:

final command = myUseCase.call.asStatekitCommand();
// Command<F, R> — pass to execute(command: command, ...)

---

How it works

executeEither is a plain extension method on StasisViewModel. It converts your function into an EitherTaskCommand<F, R> that implements Command<F, R>, then calls the existing execute method. No magic, no hidden state.

extension EitherStasisViewModelX<F, S, T extends StateObject<F, S, T>>
    on StasisViewModel<F, S, T> {
  Future<CommandResult<F, R>> executeEither<R>({
    required Future<Either<F, R>> Function() command,
    required FutureOr<void> Function(R result) onSuccess,
    FutureOr<void> Function(F failure)? onError,   // optional — defaults to setError
    FutureOr<void> Function()? onLoading,
    CommandPolicy policy = CommandPolicy.parallel,
    Object? policyKey,
  }) {
    return execute<R>(
      command: EitherTaskCommand<F, R>(command),
      onError: onError,
      onSuccess: onSuccess,
      onLoading: onLoading,
      policy: policy,
      policyKey: policyKey,
    );
  }
}

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License

MIT