expected

An extended version of C++23's std::expected<T, E> to handle variadic errors, allowing usage like expected<T, E1, E2, ...>.

Table of Contents

• Features
• Installation
• Usage
  • Basic Example
  • Advanced Example
• Contributing
• License

Features

• Compatible with C++17
• Supports multiple error types.
• Enhances standard std::expected functionality.

Installation

Clone the repository:

git clone https://github.com/mguludag/expected.git

Include the include directory in your project.

Usage (click to demo)

Basic Example

Here's a simple example of how to use expected with multiple error types:

#include <mgutility/expected.hpp>

mgutility::expected<int, std::string> divide(int a, int b) {
    if (b == 0) return mgutility::unexpected{"Division by zero"};
    return a / b;
}

int main() {
    auto result = divide(4, 2);
    if (!result) {
        // Handle error
    }
    // Use result
}

Advanced Example

Using .and_then for success and .or_else per Error Type and using .transform

• Chain operations that depend on the success of the previous one, and handle specific errors with or_else
• Transform the value inside expected if it is present

#include <mgutility/expected.hpp>
#include <iostream>
#include <string>
#include <system_error>

mgutility::expected<int, std::string, std::error_code> divide(int a, int b) {
    if (b == 0) return mgutility::unexpected<std::string>("Division by zero");
    if (a < 0) return mgutility::unexpected{std::make_error_code(std::errc::invalid_argument)};
    return a / b;
}

mgutility::expected<int, std::string, std::error_code> addOne(int x) {
    return x + 1;
}

int main() {
    auto result = divide(10, 2)
        .and_then(addOne)
        .transform([](int x) { return x * 2; })
        .or_else([](const std::string& err) -> mgutility::expected<int, std::string, std::error_code> {
            std::cerr << "String error: " << err << std::endl;
            return mgutility::unexpected<std::string>("Handled string error");
        })
        .or_else([](const std::error_code& err) -> mgutility::expected<int, std::string> {
            std::cerr << "Error code: " << err.message() << std::endl;
            return mgutility::unexpected(err.message());
        });

    if (result) {
        std::cout << "Result: " << *result << std::endl;
    } else {
      // use result.error<std::string>() or result.error()
      std::cerr << "Error: " << result.error() << std::endl;
    }
}

Contributing

Contributions are welcome! Please open issues or pull requests.

License

This project is licensed under the MIT License. See the LICENSE file for details.

This README.md provides a complete guide with basic and advanced usage examples, including multiple error types and chained handling using monadic operations.