Односвязный список. Обмен первого и последнего

#include <iostream>
#include <string>
using namespace std;
struct Node {
    string data;
    Node* next;
    Node(const string& line) : data(line), next(nullptr) {}
private:
    friend ostream& operator<<(ostream& out, const Node& node) {
        return out << node.data;
    }
};
class List {
public:
    class Iterator {
    public:
        explicit Iterator(Node* ptr) : curr(ptr) {}
        Iterator& operator++() {
            curr = curr->next;
            return *this;
        }
        string& operator*() {
            return curr->data;
        }
        const string& operator*()const {
            return curr->data;
        }
        Node* operator->() {
            return curr;
        }
        Node* operator->()const {
            return curr;
        }
        bool operator==(const Iterator& iter) {
            return curr == iter.curr;
        }
        bool operator!=(const Iterator& iter) {
            return curr != iter.curr;
        }
    private:
        Node* curr;
    };
    List() : head(nullptr), tail(nullptr) {}
    void add(const string& value) {
        auto node = new Node{ value };
        if (tail) {
            tail->next = node;
            tail = node;
        } else {
            head = tail = node;
        }
    }
    Iterator first() {
        return Iterator(head);
    }
    Iterator last() {
        return Iterator(tail);
    }
    void node_swap(Iterator& a, Iterator& b) {
        iter_swap(a, b);
    }
    Iterator begin()const {
        return Iterator(head);
    }
    Iterator end()const {
        return head != tail ? Iterator(tail->next) : Iterator(tail);
    }
private:
    Node* head;
    Node* tail;
};
void show(const List& list) {
    for (auto& item : list) cout << item << '\n';
    puts("-----");
}
int main() {
    List list;
    list.add("first");
    list.add("...");
    list.add("last");
    show(list);
    auto first = list.first();
    auto last = list.last();
    list.node_swap(first, last);
    show(list);
}