std :: chrono :: duration缺少立即滴答计数操作背后的原因是什么？

Suppose we have

假设我们有

#include <chrono>
#include <iostream>
#include <ctime>

namespace Ratios { typedef std::ratio<60*60*24,1> Days; }

typedef std::chrono::system_clock Clock;
typedef Clock::time_point TimePoint;
#include <chrono>
#in