[Question] Is the `index` field in the Archetype struct redundant? about hecs

[adamreichold]

type_ids is ordered in the same way as types, i.e. using impl Ord for TypeInfo which compares alignment, whereas index is ordered by TypeId to perform look-ups by TypeId.

IIRC, the type_ids field itself is only necessary to enable passing &[TypeId] (in contrast to &[TypeInfo]) in component order (meaning as stored in the archetype, meaning as sorted by TypeInfo).

[Ralith]

It doesn't. All component arrays are densely packed.

[Carlosted]

Thank you for your time!

[adamreichold]

(Also note that generally the cost of creating an Archetype should not be too critical as well, since if you have a workload that continuously creates new archetypes, an archetype-based ECS like hecs is probably not a good fit in the first place.)

[Carlosted]

Okay thank you very much!

If I may follow with an additional question: I have not looked at the code in depth, but it is not obvious to me why the data field stores every Data struct with an alignment of max_align (meaning the biggest alignment of all of the components present in the archetype). I probably do not understand correctly the Data struct, but it seems to me like since every component is stored in a separate array, then we could reduce space usage by using the alignment of every respective component.