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_;
  Node* ptr = head_;
  while (ptr != nullptr)
  {
    unit2 = unit2->next_;
    unit1->next_ = new Node(unit2->value_, nullptr, unit1);
    unit1 = unit1->next_;
  }
}