[mwkaufma]

> laid out next to each other in memory

Moving goalpost. But just to follow that thought: Decoupling alloc+init via e.g. placement-new to do this introduces a host of complications not considered in your solution.

If that layout _is_ a requirement, and you don't want a totally nonstandard foundation lib with nonstandard types promiscuously necessitating more nonstandard types, you want a std::vector+index handle.