Domain helpers

JIntent supplies use-case, Either and mapper helpers. Repositories, persistence, networking and caching are owned by the consuming application. The counter example’s layering (DTO, mapper, repository, use cases) is optional. Keep storage-specific types outside UI state and convert expected failures at the operation boundary.

Either is sealed, so a switch over it is checked for exhaustiveness:

final text = switch (result) {
  Left(:final value) => 'Failed: $value',
  Right(:final value) => 'Got $value',
};

Left and Right compare by value and exact runtime type (type arguments included), so equality is symmetric.

Validation

JUseCase<INPUT, OUTPUT> and JSyncUseCase<INPUT, OUTPUT> accept validators through addValidator. Each UseCaseInputValidator<I> returns Either<Exception, I>.

class PositiveCounter extends JSyncUseCase<int, int> {
  PositiveCounter() {
    addValidator((value) => value < 0
        ? Left(Exception('Counter must be non-negative'))
        : Right(value));
  }

  @override
  Either<Exception, int> run(int input) => Right(input);
}

final result = PositiveCounter().call(3);

Call the use case through call (or function-call syntax) to run validation. Calling run directly bypasses validators. Validators execute synchronously in registration order and stop at the first Left. Successful validator values are not passed to later validators or run: all receive the original input. Thrown exceptions are not converted to Left. Validators are operation preconditions, not a replacement for server-side authorization.

JUseCaseVoid exposes only run; it has no built-in validator chain. JValidationUtils (from package:jintent/utils.dart) offers parsing defaults and range checks, not a general validation framework. See the example’s validators and tests.

Mappers

JMapper<INPUT, OUTPUT> implements IMapper through a single map override:

class CountLabelMapper extends JMapper<int, String> {
  @override
  String map(int value) => 'Count: $value';
}

final mapper = CountLabelMapper();
final label = mapper.transform(2);
final labels = mapper.transformList([1, 2]);
final sameLabels = [1, 2].mapWith(mapper);

• transform converts one input; transformList returns a new output list.
• transformDynamic accepts INPUT or List<INPUT> and throws ArgumentError for other types. Prefer the typed methods when possible.
• IBiMapper<A, B> defines to(A) and from(B) for explicit two-way mapping. Implement and test both directions; invertibility is not enforced.

See the counter mapper and its tests.