Result Type for Dart

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Features

Result is a type that represents either Success or Failure.

Inspired by functional programming, Rust and Swift.

Requirements

• Dart: 3.3.0+

Install

dependencies:
  result_type: ^1.0.0

Example

The detailed example can be found at result_type/example/example.dart.

import 'dart:math';

import 'package:http/http.dart' as http;
import 'package:result_type/src/result.dart';

import 'imaginary_service.dart';
import 'photo.dart';
import 'photos_service.dart';

final client = http.Client();
final random = Random();

void main() async {
  final photosResult = await PhotosService.getPhotos(client);

  final photosOr = photosResult.unwrapOr([Photo.initial()]);

  print(photosOr);

  /// Use `switch` to handle both success and failure.
  final _ = switch (photosResult) {
    Success(value: final data) => data,
    Failure(value: final error) => 'Error: $error'
  };

  /// Do something with successful operation results or handle an error.
  if (photosResult.isSuccess) {
    print('Photos Items: ${photosResult.success}');
  } else {
    print('Error: ${photosResult.failure}');
  }

  // Chain multiple asynchronous operations.
  final result1 = await ImaginaryService.fetchData1();
  final result2 = await ImaginaryService.fetchData2(result1.success);
  final result3 = await ImaginaryService.fetchData2(result2.success);

  // Print the result of the last operation: `Success: Default Data`
  print(result3.unwrapOr('Default Data'));

  // This will throw an exception as `_handleResult`
  // has a case with 'Wrong Data'.
  //print(result3.unwrap());

  String length(String string) => string.length.toString();

  final unwrapOrElse = result3.unwrapOrElse('Default (((((Data)))))', length);
  // Print the result of the last operation: `22`
  print(unwrapOrElse);

  /// Apply transformation to successful operation results or handle an error.
  if (photosResult.isSuccess) {
    final items = photosResult
        .map(
          (i) => i.where(
            (j) => j.title.length > 60,
          ),
        )
        .success;
    print('Number of Long Titles: ${items.length}');
  } else {
    print('Error: ${photosResult.failure}');
  }

  /// In this example, note the difference in the result of using `map` and
  /// `flatMap` with a transformation that returns an result type.
  Result<int, Exception> getNextInteger() => Success(random.nextInt(4));
  Result<int, Exception> getNextAfterInteger(int n) =>
      Success(random.nextInt(n + 1));

  final nextIntegerNestedResults = getNextInteger().map(getNextAfterInteger);
  print(nextIntegerNestedResults.runtimeType);
  // Prints: Success<Result<int, Error>, dynamic>

  final nextIntegerUnboxedResults =
      getNextInteger().flatMap(getNextAfterInteger);
  print(nextIntegerUnboxedResults.runtimeType);
  // Prints: Success<int, Error>

  /// Use completion handler / callback style API if you want to.
  await PhotosService.getPhotos(client)
    ..result((photos) {
      // print('Photos: $photos');
    }, (error) {
      print('Error: $error');
    });
}

To see examples of the following package in action:

cd example && dart run

Support

Post issues and feature requests on the GitHub issue tracker.

License

The source code is distributed under the MIT license. See the LICENSE file for more info.

Libraries

result_type