How do I implement pushback for a deque using smart pointers?

I have this function definition void PushBack(const T &value);

and here are my private class members:

unsigned int cur_size;
    int capacity;
    std::unique_ptr<T[]> deque_array;
    std::unique_ptr<T[]> copy_array;
    T *head;
    T *tail;

How do I implement pushback using them? Any help would be appreciated.