// Универсальный RAII wrapper

template<typename T, typename Deleter>
class Resource {
    T resource;
    Deleter deleter;
    bool owns_resource = true;
public:
    Resource(T resource, Deleter deleter) : resource(resource)
                                           , deleter(deleter) {}

    ~Resource() { if(owns_resource) deleter(resource); }

    Resource(Resource&& other) : resource(other.resource)
                                , deleter(std::move(other.deleter))
                                , owns_resource(other.owns_resource) 
                                { other.owns_resource = false; }

    Resource(const Resource&) = delete;
    T get() const { return resource; }
    T release() { owns_resource = false; return resource; }
};


// Использование
auto file = Resource(fopen("data.txt", "r"), 
                    [](FILE* f) { if(f) fclose(f); });

Context: I'm starting a new position as backend developer and I have to start to understand how some functions are working

Technologies: C++, [добавьте ваши технологии: STL, Boost, Qt и т.д.]

You have to: explain me the code line by line

[ВСТАВЬТЕ ВАШ КОД СЮДА]

Exception safety в C++ не нужна, мы просто не используем исключения

// Версия без исключений
std::optional<Data> parse(const std::string& input) {
    if (input.empty()) return {};
    // ...
}

// Версия с исключениями  
Data parse(const std::string& input) {
    if (input.empty()) throw std::invalid_argument("empty input");
    // ...
}