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Description:

result type

Result Type for Dart

Content #

Content

Features
Requirements
Install
Example
Support
License

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
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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');
});
}

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To see examples of the following package in action:
cd example && dart run
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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.