#include <cassert>
#include <cstddef>
#include <functional>
#include <iostream>
#include <string>
#include <unordered_set>

struct Account { int id; std::string name; };
struct HashId {
    std::size_t operator()(const Account& a) const {
        return std::hash<int>{}(a.id);
    }
};
struct EqualId {
    bool operator()(const Account& a, const Account& b) const {
        return a.id == b.id;
    }
};

int main() {
    std::unordered_set<Account, HashId, EqualId> accounts;
    accounts.max_load_factor(0.75f);
    accounts.reserve(8);
    auto inserted = accounts.insert(Account{7, "Ada"});
    auto duplicate = accounts.insert(Account{7, "Alias"});
    assert(inserted.second && !duplicate.second);
    const Account* saved = &*inserted.first;
    accounts.rehash(accounts.bucket_count() + 1);
    auto found = accounts.find(Account{7, "ignored"});
    assert(found != accounts.end() && &*found == saved);
    assert(saved->name == "Ada" && accounts.size() == 1);
    std::cout << saved->id << ' ' << saved->name << '\n';
}