liburing4cpp | Modern C++ binding for liburing that features

#include 
#include 
#include 
#include 

template 
struct Promise {
    std::variant<
        std::monostate,
        std::conditional_t, std::monostate, T>,
        std::exception_ptr
    > result_;

    T await_resume() const {
        assert(result_.index() > 0);
#if 1
        // old code that I want to optimise
        if (result_.index() == 2) {
            std::rethrow_exception(std::get<2>(result_));
        }
        if constexpr (!std::is_void_v) {
            return std::get<1>(result_);
        }
#else
        // new code, won't compile
        return std::visit([](auto&& arg) {
            using TT = std::decay_t;
            if constexpr (!std::is_same_v) {
                std::rethrow_exception(arg);
            } else if constexpr (!std::is_void_v) {
                return arg;
            }
        });
#endif
    }
};

template int Promise::await_resume() const;
template std::exception_ptr Promise::await_resume() const;
template void Promise::await_resume() const;