> There are several ways to solve this problem. One way is to avoid using direct references to the particular class of objects at all. Instead, allocate a big array of objects, and refer to them with integer indexes into that array. There are several names that have been used for such arrays and indexes; let's call them arenas and handles.

I thought the term "Arena" referred to linear allocators, but maybe it's not so narrowly defined.

> At one level, this question is not very fair, because an answer to it as stated would be that one simply does not use doubly linked lists. They have been popular in introductory computer science lectures because they are a neat way to explain pointers in a data structure that's easy to draw on a whiteboard, but they are not a good match to modern hardware. The last time I used one was in the nineties. I know the Linux kernel uses them, but that design was also laid down in the nineties; if you were designing a kernel from scratch today, you would probably not do it that way.

The arena data structure you described is inefficient unless it uses a linked list to track empty slots. All general-purpose heap allocators use linked lists in their implementations. Linked lists show up wherever you want pointer stability, low fragmentation, or a way to decouple the storage of objects from their participation in data structures. I struggle to imagine how it would be possible to implement something like Linux without at least one linked list in it.

> Essentially you are bypassing the notion of pointers provided directly by the hardware

Pointers aren't a hardware concept, they're a language concept. Array indices and pointers both rely on indirect addressing, which is the underlying hardware concept. The "handles" strategy in Rust feels like a kludgy approach not because it bypasses the hardware but because Rust's borrow checker isn't actually involved in ensuring safety in that case, just its bounds checking and mandatory initialization (and if all you need is those two things then...).