#include <cassert>
#include <stdexcept>

class Transaction {
    int& target_;
    int& closed_;
    int pending_;
public:
    Transaction(int& target, int& closed, int value)
        : target_(target), closed_(closed), pending_(value) {}
    Transaction(const Transaction&) = delete;
    Transaction& operator=(const Transaction&) = delete;
    void commit() {
        if (pending_ < 0) throw std::invalid_argument("negative value");
        target_ = pending_;
    }
    ~Transaction() noexcept { ++closed_; }
};

int main() {
    int value = 4;
    int closed = 0;
    bool caught = false;
    try {
        Transaction transaction(value, closed, -1);
        transaction.commit();
    } catch (const std::invalid_argument&) {
        caught = true;
    }
    assert(caught && value == 4 && closed == 1);
    {
        Transaction transaction(value, closed, 9);
        transaction.commit();
    }
    assert(value == 9 && closed == 2);
}