c++ simple lru cache using map and double linked list

cache.cc

#include <cassert>
#include <iostream>
#include <map>
#include <string>
using namespace std;

template<class K, class V>
class cache
{
private:
    struct Entry
    {
        K key;
        V value;
        Entry *prev;
        Entry *next;
    };

    map<K, Entry*> dict;
    Entry *head, *tail;
    cache(const cache &rhs);
    cache& operator = (const cache &rhs);

    Entry* detach(Entry *entry)
    {
        entry->prev->next = entry->next;
        entry->next->prev = entry->prev;
        return entry;
    }

    void push_front(Entry *entry)
    {
        entry->next = head->next;
        entry->next->prev = entry;
        entry->prev = head;
        head->next = entry;
    }
public:
    cache() : dict()
    {
        head = new Entry();
        tail = new Entry();
        head->next = tail;
        tail->prev = head;
    }

    ~cache()
    {
        while(head->next != tail)
        {
            delete detach(head->next);
        }
        delete head;
        delete tail;
    }

    void add(const K &key, const V &value)
    {
        Entry *entry = new Entry();
        entry->key = key;
        entry->value = value;
        push_front(entry);
        dict[key] = entry;
    }

    V& get(const K &key)
    {
        Entry *entry = dict[key];
        // move to head
        detach(entry);
        push_front(entry);
        return entry->value;
    }

    void drop()
    {
        Entry* entry = detach(tail->prev);
        delete entry;
    }

    size_t size()
    {
        size_t size = 0;
        Entry *p = head;
        while(p->next != tail)
        {
            ++size;
            p = p->next;
        }
        return size;
    }
};

int main()
{
    cache<string, string> cc;
    cc.add("a", "alpha");
    cc.add("b", "bravo");
    cout << cc.get("a") << endl;
    cc.drop();
    cout << cc.get("a") << endl;
    cout << cc.size() << endl;
    return 0;
}

does this implement a map with a linked list