multiple_result

Result package for dart inspired by the work of dartz's Either and Kotlin's sealed classes.

This package is perfect to those of you who just want the Multiple results functionality from dartz. 👌

Old version:

If you're looking for a non null-safety version, you can find it in here

Use Result type:

In the return of a function, set it to return a Result type;

Result getSomethingPretty();

then add the Success and the Error types.


Result<String, Exception> getSomethingPretty() {

}

in return of the function, you just need to return

return Success('Something Pretty');

or

return Error(Exception('something ugly happened...'));

The function should look something like this:


Result<String, Exception> getSomethingPretty() {
    if(isOk) {
        return Success('OK!');
    } else {
        return Error(Exception('Not Ok!'));
    }
}

Handling the Result with when

void main() {
    final result = getSomethingPretty();
     final String message = result.when(
         (error) {
          // handle the error here
          return "error";
        }, (success) {
          // handle the success here
          return "success";
        },
    );

}

Handling the Result with onSuccess or onError

    final result = getSomethingPretty();
    // notice the [onSuccess] or [onError] will only be executed if
    // the result is a Success or an Error respectivaly. 
    final output = result.onSuccess((name) {
        // handle here the success
        return "";
    });
    
    final result = getSomethingPretty();
    
    // [result] is NOT an Error, this [output] will be null.
    final output = result.onError((exception) {
        // handle here the error
        return "";
    });

Handling the Result with get

note: [get] is now deprecated and will be removed in the next version.

void main() {
    final result = getSomethingPretty();

    String? mySuccessResult;
    if (result.isSuccess()) {
      mySuccessResult = result.get();
    }
}

Handling the Result with tryGetSuccess

void main() {
    final result = getSomethingPretty();

    String? mySuccessResult;
    if (result.isSuccess()) {
      mySuccessResult = result.tryGetSuccess();
    }
}

Handling the Result with tryGetError

void main() {
    final result = getSomethingPretty();

    Exception? myException;
    if (result.isError()) {
      myException = result.tryGetError();
    }
}

Mapping success value with map

void main() {
    final result = getResult()
                    .map((e) => MyObject.fromMap(e));

    result.tryGetSuccess(); //Instance of 'MyObject' 
}

Mapping error value with mapError

void main() {
    final result = getResult()
                    .mapError((e) => MyException(e));

    result.tryGetError(); //Instance of 'MyException'

}

Chain others Result with flatMap


Result<String, MyException> checkIsEven(String input){
    if(input % 2 == 0){
        return Success(input);
    } else {
        return Error(MyException('isn`t even!'));
    }
}

void main() {
    final result = getNumberResult()
                    .flatMap((s) => checkIsEven(s));
}

Add a pure 'Success' value with pure

void main() {
    final result = getSomethingPretty().pure(10);

    String? mySuccessResult;
    if (result.isSuccess()) {
      mySuccessResult = result.tryGetSuccess(); // 10
    }
}

Unit Type

Some results do not need a specific return. Use the Unit type to signal an empty return.

    Result<Unit, Exception>

Use AsyncResult type:

AsyncResult<S, E> represents an asynchronous computation. Use this component when working with asynchronous Result.

AsyncResult has some of the operators of the Result object to perform data transformations (Success or Error) before executing the Future.

The operators of the Result object available in AsyncResult are:

  • map
  • mapError
  • flatMap
  • pure

AsyncResult<S, E> is a typedef of Future<Result<S, E>>.


AsyncResult<String, Exception> fetchProducts() async {
    try {
      final response = await dio.get('/products');
      final products = ProductModel.fromList(response.data);
      return Success(products);
    } on DioError catch (e) {
      return Error(ProductException(e.message));
    }
}

...

final state = await fetch()
    .map((products) => LoadedState(products))
    .mapLeft((error) => ErrorState(error))

Libraries

multiple_result