template <typename T>
T& List<T>::find(T& data)
{
     Node<T> * curr = first;
     bool isFound = false;
     while(curr != nullptr)
     {
         if(curr->data == &data || curr->next->data == &data)
         {
             isFound = true;
             break;
         }
         curr = curr->next;
     }
     if(isFound) return *(curr->data);
     else throw std::invalid_argument("no such item");
 }