Chrono ostream

chrono_ostream.hpp

template <typename Period2, typename Rep, typename Period>
constexpr auto fractional_count(const std::chrono::duration<Rep, Period>& duration)
{
    return std::chrono::duration<double, Period2>(duration).count();
}

template <typename Rep, typename Period>
std::ostream& operator<<(std::ostream& out, const std::chrono::duration<Rep, Period>& duration)
{
    namespace ch = std::chrono;

    if (ch::duration_cast<ch::seconds>(duration).count() > 0)
        return out << fractional_count<std::ratio<1>>(duration) << "s";
    else if (ch::duration_cast<ch::milliseconds>(duration).count() > 0)
        return out << fractional_count<std::milli>(duration) << "ms";
    else if (ch::duration_cast<ch::microseconds>(duration).count() > 0)
        return out << fractional_count<std::micro>(duration) << "us";
    else if (ch::duration_cast<ch::nanoseconds>(duration).count() > 0)
        return out << fractional_count<std::nano>(duration) << "ns";
}