Method expand

base_code/template.cpp:279–296

    Alloc _allocator;

    void expand()
    {
        int size = _end - _first;
        T *ptmp = _allocator.allocate(2 * size); // 分配 2*size 大小内存
        int len = _last - _first;
        for (int i = 0; i < size; ++ i) { // 构造 size 个有效的T对象
            _allocator.construct(ptmp + i, _first[i]);
        }

        // 先析构再free
        for (T *p = _first; p != _last; ++ p) {
            _allocator.destroy(p);
        }
        _allocator.deallocate(_first);
        _first = ptmp;
        _last = _first + size;
        _end = _first + 2 * size;
    }
};

/* 测试类 */