void add_noopt()
{
    value_t temp(gen_value());
    v.push_back(temp);
}

void add_opt()
{
    v.push_back(gen_value());
}

template <typename AddFn> void test2(AddFn fn)
{
    const size_t N = 1000000;
    v.clear();
    boost::posix_time::ptime t1 = boost::posix_time::microsec_clock::universal_time();
    for(size_t i = 0; i < N; ++i) {
        fn();
        v.clear(); // consume generated value
    }
    boost::posix_time::ptime t2 = boost::posix_time::microsec_clock::universal_time();
    cout << (t2-t1) << endl;

}

int main()
{
    test2(add_noopt);
    test2(add_opt);
    test2(add_noopt);
    test2(add_opt);

    return 0;
}