Return a result ErrorOr with either a value T or an error Object
ErrorOr
Return a result ErrorOr with either a value T or an error Object.
Features
Always return a value ErrorOr from an async function. Let the called function
handle the error and return an ErrorOr. The caller can then await the result
without a try catch.
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 a private subclass of ErrorOr, either a _ValueWrapper
or an _ErrorWrapper, with the expected non-null value.
ErrorOr can be used for non-async functions too – for both Flutter and Dart.
Getting started
Make a function return a Future<ErrorOr>, which you’ll await in the calling
function.
Create a ErrorOr instance by calling one of its factory constructors value
or error.
Check hasError or hasValue, before calling error or value. If either is
called without the proper check, a ErrorOrTypeError is thrown.
Usage
Example
Future<ErrorOr<LocationPermission>> checkPermission() async {
try {
return ErrorOr.value(await Geolocator.checkPermission());
} catch (e) {
return ErrorOr.error(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 pattern was inspired by result_type.