Thread safe Unique ID Generator in c++ using std::atomic

UniqueIDGenerator.cpp

template <typename T>
struct UniqueIDGenerator {
    std::atomic<T> _id;
    std::function<const T(const T&)> _nexter;

    template <typename NEXT>
    UniqueIDGenerator(const T& init, const NEXT& nexter) {
        _id.store(init, std::memory_order::memory_order_release);
        _nexter = nexter;
    }

    const T fetch_add() {
        T oldVal;
        T newVal;
        do {
            oldVal = _id;
            newVal = _nexter(oldVal);
        } while (!_id.compare_exchange_weak(oldVal, newVal));
        return oldVal;
    }
};