OpResult #

A lightweight, type-safe result wrapper for handling success and failure cases in Dart.

Features #

OpResult is a generic class designed to handle operations that return either a success or a failure in a structured and type-safe manner.

• Generic over Success and Error Types (OpResult<T, E>)
• Prevents null checks—ensures only one of data or error exists
• Encapsulates errors in a structured way using enums
• Easily maps error types to custom/multi-language messages
• Works seamlessly in any context, with APIs, validation, domain logic, etc.
• No dependencies—lightweight and efficient

Getting started #

Add op_result to your project’s pubspec.yaml:

dart pub add op_result
or
flutter pub add op_result

Usage #

Basic Success & Failure Handling

import 'package:op_result/op_result.dart';

enum ApiError {
  networkFailure,
  unauthorized,
  notFound,
}

void main() {
  final successResult = OpResult.success("User fetched successfully");
  final failureResult = OpResult.failure(ApiError.notFound);

  if (successResult.isSuccess) {
    print("Success: ${successResult.data}");
  }

  if (failureResult.isFailure) {
    print("Error: ${failureResult.error}");
  }
}

API Call Example

Future<OpResult<User, ApiError>> fetchUser() async {
  final response = await apiClient.get("/user");

  if (response.statusCode == 200) {
    return OpResult.success(User.fromJson(response.body));
  }

  return OpResult.failure(ApiError.notFound);
}

void main() async {
  final result = await fetchUser();

  result.isSuccess
      ? print("User: ${result.data}")
      : print("Failed: ${result.error}");
}

Form Validation Example

OpResult<void, ValidationError> validatePassword(String password) {
  if (password.isEmpty) {
    return OpResult.failure(ValidationError.empty);
  }

  if (password.length < 6) {
    return OpResult.failure(ValidationError.tooShort);
  }

  return OpResult.success(null);
}

void main() {
  final result = validatePassword("123");

  result.isFailure
      ? print("Validation Error: ${result.error}")
      : print("Password is valid!");
}

Custom Error Messages

import 'package:op_result/op_result.dart';

enum AuthError {
  invalidCredentials,
  accountLocked,
  serverError,
}

// Example message mapping (could be loaded from a localization system)
const Map<AuthError, String> errorMessages = {
  AuthError.invalidCredentials: "Invalid username or password.",
  AuthError.accountLocked: "Your account has been locked. Please contact support.",
  AuthError.serverError: "An error occurred on the server. Try again later.",
};

OpResult<void, AuthError> authenticate(String username, String password) {
  if (username != "admin" || password != "password123") {
    return OpResult.failure(AuthError.invalidCredentials);
  }
  return OpResult.success(null);
}

void main() {
  final result = authenticate("user", "wrongpass");

  if (result.isFailure) {
    print("Error: ${errorMessages[result.error]!}"); 
  }
}

License #

This package is licensed under the BSD 3-Clause License. See the LICENSE file for details.