Indexable priority queue (C++17)

indexable_pq.hpp

#include <initializer_list>
#include <queue>
#include <vector>

template <typename T, typename Cmp>
struct indexable_queue : public std::priority_queue<T, std::vector<T>, Cmp>
{
    T& at(std::size_t index) { return this->c.at(index); }
    const T& at(const std::size_t index) const { return this->c.at(index); }
    
    indexable_queue() = default;
    indexable_queue(std::initializer_list<T> items, Cmp cmp = Cmp{})
        : std::priority_queue<T, std::vector<T>, Cmp>(cmp, std::vector<T>{items}) {}
};

test_indexable_pq.cpp

#include "indexable_pq.hpp"

#include <string>
#include <tuple>

struct Item{
    int price;
    std::string name;
};

struct ItemCmp{
    bool operator()(const Item& lhs, const Item& rhs) const {
        return std::tie(lhs.price, lhs.name) > std::tie(rhs.price, rhs.name);
    }
};

int main() {
    indexable_queue<Item, ItemCmp> items({{10, "Pizza"}, {5, "Coffee"}, {20, "Chocolate"}});

    for (std::size_t index {0UL}; index < items.size(); ++index)
    {
        std::cout << items.at(index).name << '\n';
    }
  
    /*
      output:
        Coffee
        Pizza
        Chocolate
    */
}