#include <vector>

    class TimerFriend
    {
    public:
      TimerFriend(const TimerFriend&) = default;
      TimerFriend& operator =(const TimerFriend&) = default;
    
    private:
      TimerFriend() {}
    
      friend class Timer;
    };

    class Timer {
        private:
            int timeLeft;
    
        public:
            Timer(unsigned int ms, const TimerFriend&) : timeLeft(ms) {}

            static std::vector<Timer> instances;
            static void create(unsigned int ms) {
                instances.emplace_back(ms, TimerFriend());
            }
    };
    
    std::vector<Timer> Timer::instances;

int main()
{
    Timer::create(100);
}