template <class T>
QueueList<T>::QueueList(const QueueList<T>& src)
{
    head_ = new Node(src.head_->value_, nullptr, nullptr);
    Node* unit1 = head_;
    Node* unit2 = src.head_;
    while (unit2->next_ != nullptr)
    {
        unit2 = unit2->next_;
        unit1->next_ = new Node(unit2->value_, nullptr, unit1);
        unit1 = unit1->next_;
    }
    tail_ = unit1;
}