Method pop

include/fplus/queue.hpp:29–38

    {
    }
    fplus::maybe<T> pop()
    {
        std::unique_lock<std::mutex> lock(mutex_);
        if (queue_.empty()) {
            return {};
        }
        auto item = queue_.front();
        queue_.pop_front();
        return item;
    }

    void push(const T& item)
    {