LRU C++17

class LRUCache {
public:
    LRUCache(int c)
        : capacity{size_t(c)}
    {}

    int get(int key) const
    {
        auto it = cache.find(key);
        if (it == std::end(cache)) {
            return -1;
        }
        lru.splice(std::cend(lru), lru, *it->second.lru);
        return it->second.value;
    }

    void put(int key, int value)
    {
        auto it = cache.find(key);
        if (it == std::end(cache)) {
            it = cache.insert(it, {key, Value{value, nullptr}});
            if (cache.size() > capacity) {
                cache.erase(lru.front());
                lru.splice(std::cend(lru), lru, std::cbegin(lru));
                lru.back() = it;
            } else {
                lru.push_back(it);
            }
            it->second.lru = std::make_unique<Iterator>(std::prev(std::end(lru)));
        } else {
            it->second.value = value;
            lru.splice(std::cend(lru), lru, *it->second.lru);
        }
    }
private:
    struct Iterator;
    struct Value
    {
        int value;
        std::unique_ptr<Iterator> lru;
    };
    using Cache = std::unordered_map<int /* key */, Value>;
    using LRU = std::list<typename Cache::iterator>;
    struct Iterator : LRU::iterator
    {
        Iterator(LRU::iterator it)
            : LRU::iterator{it}
        {}
    };

    const size_t capacity;
    Cache cache;
    mutable LRU lru;
};