template<typename T, typename Y> auto operator+(std::optional<T> lhs, std::optional<Y> rhs) -> std::optional<decltype(*lhs + *rhs)> {
    if (!lhs || !rhs)
        return none;
    return *lhs + *rhs;
}

std::optional<T> f() {
    auto x = something();
    auto x2 = something_else();
    return x + x2;
}