so the physical layout has a bit vector with one bit for each optional. and a popcnt over that bitvector (masked up to the value we're interested in) will give the actual slot to look into?

would also make sense to reorder / bucket fields by (byte) size

if you want to do that in any low level language (rust, c++) you have to deviate from their standard syntax for optionals, and you have to manually keep track of slot order. but for domains with many optional/default values, this amy really reduce cache pressure, no?

In higher level languages you can fake the effect (with flyweight facades), so from python such a packed "dataclass"-like class can look neat and clean. however at the low level there is no abstraction that allows to create your own data layout.

at least I didn't find anything yet.