Either

The library for Error Handling.

main() async {
  // There is some method that will return the user or error.
  await getUser()
    ..either((ServerError error) {
      // Add a handler for the error.
      print("Error: ${error.code}");
    }, (User user) {
      // Add a handler to get the user.
      print("User: ${user.name}");
    });

  // or
  final either = await getUser();
  if (either.isLeft) {
    final error = either.left;
    print("Error: ${error.code}");
  } else {
    final user = either.right;
    print("User: ${user.name}");
  }
}

// And the return of either looks like this.
// According to the agreement, the right part stores the result of success,
// left is wrong.
Future<Either<ServerError, User>> getUser() async =>
    (Random().nextBool()) ? Right(User("Bob")) : Left(ServerError(500));

Installation

Add on pubspec.yml:

dependencies:
  either_type: ^0.1.2

Getting Started

This project is a starting point for a Dart package, a library module containing code that can be shared easily across multiple Flutter or Dart projects.

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