rsl 1.0.0

A simple Result type implementation for Dart with standalone Right/Left constructors similar to dartz.

example/rsl_example.dart

// rsl_example.dart
import 'package:rsl/rsl.dart';

void main() {
  // 1. Basic Usage
  print('\n=== Basic Usage ===');
  final validNumber = parseNumber('42');
  final invalidNumber = parseNumber('abc');

  printResult(validNumber); // Success: 42
  printResult(invalidNumber); // Error: Invalid number: abc

  // 2. Different Ways to Handle Results
  print('\n=== Handling Results ===');
  handleResults();

  // 3. Chaining Operations
  print('\n=== Chaining Operations ===');
  chainOperations();

  // 4. Real-world Example: API Call
  print('\n=== Real-world Example ===');
  simulateApiCall();
}

// 1. Basic Usage Example
Result<String, int> parseNumber(String input) {
  try {
    return Right(int.parse(input));
  } catch (e) {
    return Left('Invalid number: $input');
  }
}

void printResult(Result<String, int> result) {
  result.fold(
    (error) => print('Error: $error'),
    (number) => print('Success: $number'),
  );
}

// 2. Different Ways to Handle Results
void handleResults() {
  final success = Right<String, int>(42);
  final failure = Left<String, int>('Something went wrong');

  // Using fold (pattern matching)
  print('Using fold:');
  success.fold(
    (error) => print('Failure: $error'),
    (value) => print('Success: $value'),
  );

  // Using getOrElse
  print('\nUsing getOrElse:');
  print('Success value: ${success.getOrElse(() => 0)}');
  print('Failure value: ${failure.getOrElse(() => 0)}');

  // Using getOrNull
  print('\nUsing getOrNull:');
  print('Success value: ${success.getOrNull()}');
  print('Failure value: ${failure.getOrNull()}');

  // Using getOrThrow
  print('\nUsing getOrThrow:');
  try {
    print('Success value: ${success.getOrThrow()}');
    print('Failure value: ${failure.getOrThrow()}'); // This will throw
  } catch (e) {
    print('Caught error: $e');
  }
}

// 3. Chaining Operations
void chainOperations() {
  final result = Right<String, String>('hello,world')
      .map((s) => s.split(',')) // Returns List<String>
      .flatMap((list) {
        // Explicit null check and length validation
        if (list.isEmpty || list.length < 2) {
          return Left<String, List<String>>('Invalid format: expected 2 parts');
        }
        return Right<String, List<String>>(list);
      })
      .map((list) {
        // Safe access since flatMap ensured we have at least 2 elements
        final first = list[0];
        final second = list[1];
        return '$first ${second.toUpperCase()}';
      });

  print('Final result:');
  result.fold(
    (error) => print('Error: $error'),
    (value) => print('Value: $value'),
  );

  // Swapping example
  print('\nAfter swap:');
  final swapped = result.swap();
  swapped.fold(
    (error) => print('Error: $error'),
    (value) => print('Value: $value'),
  );
}

// 4. Real-world Example: API Call
void simulateApiCall() {
  // Simulate a user repository
  final userRepo = UserRepository();

  // Successful case
  print('Fetching valid user:');
  userRepo
      .getUser(123)
      .fold(
        (error) => print('Error: $error'),
        (user) => print('User: ${user.name} (${user.email})'),
      );

  // Error case
  print('\nFetching invalid user:');
  userRepo
      .getUser(999)
      .fold((error) => print('Error: $error'), (user) => print('User: $user'));
}

// Supporting classes for the real-world example
class User {
  final int id;
  final String name;
  final String email;

  User(this.id, this.name, this.email);
}

class UserRepository {
  final _users = {
    123: User(123, 'John Doe', '[e-mail]'),
    456: User(456, 'Jane Smith', '[e-mail]'),
  };

  Result<String, User> getUser(int id) {
    return _users.containsKey(id)
        ? Right(_users[id]!)
        : Left('User with ID $id not found');
  }
}