vector::emplace_back for objects with a private constructor

Question

I want my Timer objects to be created via Timer::create() only. For this purpose, I made the constructor private. However, I get a compiler error saying that \"Timer::Timer(

Answer 1

You probably should implement your own allocator, that will be friend to timer:

class Timer {

    struct TimerAllocator: std::allocator
    {
        template< class U, class... Args >
        void construct( U* p, Args&&... args )
        {
            ::new((void *)p) U(std::forward(args)...);
        }

        template< class U > struct rebind { typedef TimerAllocator other; };

    };
    friend class TimerAllocator;

    private:
        int timeLeft;

    Timer(unsigned int ms) : timeLeft(ms) 
    {}

    public:
        static std::vector instances;
        static void create(unsigned int ms) {
            instances.emplace_back(ms);
        }
};

std::vector Timer::instances;

int main()

{
    Timer::create(100);
}

The simplest solution would be derive from std::allocator reimplementing rebind to rebind to itself, so vector couldn't rebind allocator back to std::allocator and implement own construct to actually create Timers.