push_front.cpp

void push_front(const Data &data)
{
    // if the list is empty we're going to add head
    if (isEmpty())
    {
        head = std::make_unique<Node>(data, nullptr);
    }
    else
    {
        node_ptr newNode = std::make_unique<Node>(data, nullptr);
        newNode->next = std::move(head);
        head = std::move(newNode);
    }
    size++;
};