Author

This package was created by Michael Piper. You can reach out via email at pipermichael@aol.com

Result Library

A robust Result<T, E> type implementation for handling success and error states in Flutter and Dart applications. Inspired by functional programming paradigms, this library provides a clean and type-safe way to manage operations that may succeed or fail.

Why Use This Package?

Type-Safe Error Handling: Avoid runtime errors by explicitly handling success (Ok) and failure (Err) cases.
Functional Programming Style: Encourages immutability and composability, making your code more predictable and easier to debug.
Flutter-Friendly: Designed with Flutter in mind, this library integrates seamlessly into your app's architecture.
Comprehensive API: Includes methods like isOk, isErr, unwrap, and unwrapErr for flexible error handling.

Installation

Add the following to your pubspec.yaml:

dependencies:
  result_library: ^1.0.0

Then run:

flutter pub get

Usage

Basic Example

import 'package:result_library/result_library.dart';

void main() {
  // Success case
  Result<int, String> success = Ok(42);
  print(success.isOk()); // true
  print(success.unwrap()); // 42
  print(success.ok()); // 42

  // Error case
  Result<int, String> failure = Err('Something went wrong');
  print(failure.isErr()); // true
  print(failure.unwrapErr()); // Something went wrong
  print(failure.err()); // Something went wrong
}

Pattern Matching with `when`

final r = Ok<int, String>(5);
final value = r.when(
  ok: (v) => v,        // keep the success value
  err: (e) => 0,       // provide a fallback value of type T
);
print(value); // 5

Asynchronous `fold<R>()`

final r2 = Err<int, String>('network');
final message = await r2.fold<String>(
  ok: (v) async => 'ok: $v',
  err: (e) async => 'err: $e',
);
print(message); // "err: network"

Transforming with `map<RT>()`

final r3 = Ok<int, String>(7);
final mapped = r3.map((v) => 'value=$v'); // Result<String, String>
print(mapped.isOk()); // true
print(mapped.ok()); // "value=7"

Advanced Example

import 'package:result_library/result_library.dart';

Result<int, String> divide(int a, int b) {
  if (b == 0) {
    return Err('Division by zero');
  }
  return Ok(a ~/ b);
}

void main() {
  final result = divide(10, 2);

  if (result.isOk()) {
    print('Result: ${result.unwrap()}'); // Result: 5
  } else {
    print('Error: ${result.unwrapErr()}'); // Handles division by zero
  }
   if (result.isOk()) {
    print('Result: ${result.ok()}'); // Result: 5
  } else {
    print('Error: ${result.err()}'); // Handles division by zero
  }

  if (result.isErr()) {
    print('Error: ${result.err()}'); // Error: Division by zero
  } else {
    print('Result: ${result.ok()}'); // Result: 5
  }
}

To expand the use cases of the result_library package, we can cover a variety of scenarios such as API calls, file operations, and more complex error handling. Below are additional examples that demonstrate how the Result<T, E> type can be used in different contexts.

1. API Call Example

This example demonstrates how to handle API responses using the Result<T, E> type. It simulates fetching data from an API and handling success or failure cases.

import 'dart:convert';
import 'package:http/http.dart' as http;
import 'package:result_library/result_library.dart';

Future<Result<Map<String, dynamic>, String>> fetchUserData(String userId) async {
  final url = Uri.parse('https://api.example.com/users/$userId');

  try {
    final response = await http.get(url);

    if (response.statusCode == 200) {
      // Parse the JSON response
      final Map<String, dynamic> data = json.decode(response.body);
      return Ok(data);
    } else {
      // Handle HTTP errors
      return Err('Failed to fetch user data: ${response.statusCode}');
    }
  } catch (e) {
    // Handle network or parsing errors
    return Err('An error occurred: $e');
  }
}

void main() async {
  final result = await fetchUserData('123');

  if (result.isOk()) {
    print('User Data: ${result.unwrap()}');
  } else {
    print('Error: ${result.unwrapErr()}');
  }
}

Explanation:

The fetchUserData function returns a Result<Map<String, dynamic>, String>.
If the API call succeeds, it returns an Ok with the parsed JSON data.
If the API call fails (e.g., due to network issues or invalid status code), it returns an Err with an error message.

2. File Operations Example

This example demonstrates how to handle file reading operations using the Result<T, E> type.

import 'dart:io';
import 'package:result_library/result_library.dart';

Result<String, String> readFile(String filePath) {
  try {
    final file = File(filePath);
    if (!file.existsSync()) {
      return Err('File not found: $filePath');
    }

    final content = file.readAsStringSync();
    return Ok(content);
  } catch (e) {
    return Err('Error reading file: $e');
  }
}

void main() {
  final result = readFile('example.txt');

  if (result.isOk()) {
    print('File Content: ${result.unwrap()}');
  } else {
    print('Error: ${result.unwrapErr()}');
  }
}

Explanation:

The readFile function attempts to read the contents of a file.
If the file exists and is successfully read, it returns an Ok with the file content.
If the file does not exist or an error occurs, it returns an Err with an appropriate error message.

3. Validation Example

This example demonstrates how to validate user input using the Result<T, E> type.

import 'package:result_library/result_library.dart';

Result<int, String> validateAge(String input) {
  final age = int.tryParse(input);

  if (age == null) {
    return Err('Invalid input: Age must be a number');
  }

  if (age < 0 || age > 120) {
    return Err('Invalid age: Must be between 0 and 120');
  }

  return Ok(age);
}

void main() {
  final inputs = ['25', '-5', 'abc'];

  for (final input in inputs) {
    final result = validateAge(input);

    if (result.isOk()) {
      print('Valid age: ${result.unwrap()}');
    } else {
      print('Error: ${result.unwrapErr()}');
    }
  }
}

Explanation:

The validateAge function checks if the input is a valid integer and falls within a reasonable range.
If the input is valid, it returns an Ok with the parsed age.
If the input is invalid, it returns an Err with an appropriate error message.

4. Chained Operations Example

This example demonstrates how to chain multiple operations using the Result<T, E> type.

import 'package:result_library/result_library.dart';

Result<int, String> calculateSquare(int value) {
  if (value < 0) {
    return Err('Value cannot be negative');
  }
  return Ok(value * value);
}

Result<int, String> addTen(int value) {
  return Ok(value + 10);
}

void main() {
  final input = 5;

  final result = calculateSquare(input)
      .map((square) => addTen(square).unwrap());

  if (result.isOk()) {
    print('Final Result: ${result.unwrap()}');
  } else {
    print('Error: ${result.unwrapErr()}');
  }
}

Explanation:

The calculateSquare function squares the input value if it's non-negative.
The addTen function adds 10 to the input value.
The operations are chained using .map, which allows you to transform the success value while propagating errors.

5. Complex Error Handling Example

This example demonstrates how to handle multiple error types and provide detailed error messages.

import 'package:result_library/result_library.dart';

enum DivisionError { divisionByZero, invalidInput }

Result<int, DivisionError> safeDivide(int a, int b) {
  if (b == 0) {
    return Err(DivisionError.divisionByZero);
  }
  if (a < 0 || b < 0) {
    return Err(DivisionError.invalidInput);
  }
  return Ok(a ~/ b);
}

void main() {
  final result = safeDivide(10, 0);

  if (result.isOk()) {
    print('Result: ${result.unwrap()}');
  } else {
    switch (result.unwrapErr()) {
      case DivisionError.divisionByZero:
        print('Error: Division by zero');
        break;
      case DivisionError.invalidInput:
        print('Error: Invalid input');
        break;
    }
  }
}

Explanation:

The safeDivide function handles two types of errors: division by zero and invalid input.
The error type is represented as an enum, making it easy to handle different error cases.

6. Combining Multiple Results

This example demonstrates how to combine multiple Result values into a single result.

import 'package:result_library/result_library.dart';

Result<int, String> multiply(int a, int b) {
  if (a < 0 || b < 0) {
    return Err('Inputs must be non-negative');
  }
  return Ok(a * b);
}

Result<int, String> add(int a, int b) {
  return Ok(a + b);
}

void main() {
  final result1 = multiply(3, 4);
  final result2 = add(5, 7);

  if (result1.isOk() && result2.isOk()) {
    final combinedResult = result1.unwrap() + result2.unwrap();
    print('Combined Result: $combinedResult');
  } else {
    print('Error: ${result1.isErr() ? result1.unwrapErr() : result2.unwrapErr()}');
  }
}

Explanation:

Two operations (multiply and add) are performed independently.
Their results are combined only if both succeed. Otherwise, the first error encountered is reported.

Conclusion

These examples showcase the versatility of the Result<T, E> type in handling various scenarios such as API calls, file operations, validation, chaining, and error handling. By using this pattern, you can write robust, type-safe, and maintainable Dart code that gracefully handles success and failure cases.

You can include these examples in your package's documentation or README.md to help users understand how to use the library effectively.

API Reference

Result<T, E>: Represents either a successful value (Ok) or an error (Err).
isOk(): Returns true if the result is Ok.
isErr(): Returns true if the result is Err.
ok(): Retrieves the success value. Throws an exception if called on an Err.
err(): Retrieves the error value. Throws an exception if called on an Ok.
unwrap(): Unwraps the success value. Throws an exception if the result is Err.
unwrapErr(): Unwraps the error value. Throws an exception if the result is Ok.
when({required T Function(T) ok, required T Function(E) err}): Pattern-match and produce a T in both branches.
fold<R>({required Future<R> Function(T) ok, required Future<R> Function(E) err}): Asynchronously fold into a Future<R>.
map<RT>(RT Function(T)): Transform the Ok value to a new type, preserving E.

Author

Result Library

Why Use This Package?

Installation

Usage

Basic Example

Pattern Matching with `when`

Asynchronous `fold<R>()`

Transforming with `map<RT>()`

Advanced Example

1. API Call Example

2. File Operations Example

3. Validation Example

4. Chained Operations Example

5. Complex Error Handling Example

6. Combining Multiple Results

Conclusion

API Reference

Contributing

License

MIT License

result-library-dart

result-library-dart

result-library-dart

result-library-dart

Libraries

result_library package

Author

Result Library

Why Use This Package?

Installation

Usage

Basic Example

Pattern Matching with when

Asynchronous fold<R>()

Transforming with map<RT>()

Advanced Example

1. API Call Example

2. File Operations Example

3. Validation Example

4. Chained Operations Example

5. Complex Error Handling Example

6. Combining Multiple Results

Conclusion

API Reference

Contributing

License

MIT License

result-library-dart

result-library-dart

result-library-dart

result-library-dart

Libraries

result_library package

Pattern Matching with `when`

Asynchronous `fold<R>()`

Transforming with `map<RT>()`