This is very similar to what std::deque does under the covers already. It's a chunked array. The main difference AFAICT from std::deque is that this offers n^1/2 insertion and deletion within the body of the array. This guarantee is provided by allowing for the possibility of significant overallocation in the chunks themselves, if many modifications happen in the middle of the array. On the other hand, std::deque does not overallocate by as much -- just a chunk at the beginning and a chunk at the end. But as a consequence it has to move trailing elements when an element is inserted or deleted in the middle.

Interesting!