cpp_result

A Rust-inspired Result<T, E> type for C++20 and later.

Features

• Ok<T> / Err<E> result values
• void specializations
• lvalue reference support
• functional chaining via map, map_err, and_then, and or_else
• niche optimization for selected Result<T, void> / Result<void, E> cases
• freestanding mode via RESULT_FREESTANDING

Requirements

C++20 or later.

Freestanding

Define RESULT_FREESTANDING before including the header when building for a kernel or another freestanding target:

#define RESULT_FREESTANDING
#include <result/result.hpp>

In this mode the header avoids hosted-only dependencies such as <iostream>, <stdexcept>, <variant>, and exception-based APIs. Error paths use RESULT_ERROR(message), and assertions use RESULT_ASSERT(condition). Define those macros before including the header if your kernel has its own panic or assert implementation.

unwrap_or_throw() is only available for hosted builds with exceptions enabled. The multi_optional hosted std::variant fallback is disabled in freestanding mode, so its alternatives must share an implicitly discoverable niche.

Installation

include(FetchContent)

FetchContent_Declare(
        result
        GIT_REPOSITORY https://github.com/LuisRuisinger/cpp_result.git
        GIT_TAG v0.1.0
)

FetchContent_MakeAvailable(result)

target_link_libraries(your_target PRIVATE lsr::result)

Include:

#include <result/result.hpp>

Basic Usage

#include <iostream>
#include <string>

#include <result/result.hpp>

using namespace lsr::result;

Result<float, std::string> divide(int a, int b) {
    if (b == 0)
        return Err(std::string("division by zero"));

    return Ok(static_cast<float>(a) / b);
}

int main() {
    auto result = divide(10, 2);

    if (result.is_ok())
        std::cout << result.unwrap_ref() << '\n';

    return 0;
}

Notes

Consuming methods such as unwrap, unwrap_err, map, and and_then are &&-qualified:

auto value = std::move(result).unwrap();

Inspection methods such as is_ok, is_err, unwrap_ref, and unwrap_err_ref do not consume the result.

Headers under result/detail/ are implementation details and are not part of the public API.

License

MIT. See LICENSE.