Does std::vector *have* to move objects when growing capacity? Or, can allocators “reallocate”?

Question

A different question inspired the following thought:

Does std::vector have to move all the elements when it increases its capacity?

Answer 1

When std::vector runs out of capacity it has to allocate a new block. You have correctly covered the reasons.

IMO it would make sense to augment the allocator interface. Two of us tried to for C++11 and we were unable to gain support for it: [1] [2]

I became convinced that in order to make this work, an additional C-level API would be needed. I failed in gaining support for that as well: [3]