Mixed boxed/unboxed arrays?

[J. Reinders]

> Could you use `StablePtr` for the keys?

That might be an option, but I have no idea how performant stable pointers are and manual management is obviously not ideal.

> How does the cost of computing object hashes and comparing colliding
> objects compare with the potential cache miss cost of using boxed
> integers or a separate array?  Would such an "optimisation" be worth
> the effort?

Literature on hash tables suggests that cache misses were a very important factor in running time (in 2001): https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.25.4189

I don’t know whether it has become less or more important now, but I have been told there haven’t been that many advances in memory latency.