error_or 0.0.2

A result class for returning a value or an error

ErrorOr

A simple package for returning a result with either a value T or an error Object.

Features

Return a value ErrorOr from an async function and await it without a try catch - and rather do that in the called function.

A subclass of ErrorOr contains either the expected value T or an error Object (usually an Exception returned from a try catch).

Internally, we create one of two hidden subbclasses of ErrorOr, either a _Success or a _Failure, which contains the expected non-null values.

ErrorOr can be used for non-async (sync) functions too - for both Flutter and Dart.

Getting started

Make a function return a Future<ErrorOr>, which you'll await in the calling class.

Create a ErrorOr type by calling one of its factory methods withValue or withError.

Check if hasError, before calling error, or check if hasValue before calling value. If either is called without the proper check, an ErrorOrTypeCastError is thrown.

Usage

Example

Future<ErrorOr<LocationPermission>> checkPermission() async {
  try {
    return ErrorOr.withValue(await Geolocator.checkPermission());
  } catch (e) {
    return ErrorOr.withError(e);
  }
}
ErrorOr<LocationPermission> errorOrPermission = await checkPermission();
if (errorOrPermission.hasError) {
	return errorOrPermission;
}
LocationPermission permission = errorOrPermission.value;

Additional information

I would like to keep this package minimal, but please get in touch on github if you have suggestions to improvements.

The name was inspired by the ErrorOr type of SerenityOS.

The Success / Failure type pattern was inspired by result_type.