Do I have to care about in which order to put data members of a struct in order to get optimal memory alignment packing or does Julia optimize the order automatically?
AFAICT it doesn’t because
prints 24. If it did pack and reorder members into the order x,y,z it would print 16 on a 64-bit machine.
Generally, Julia mirrors the C layout, so the same principles apply.
(Also, it seems that you are asking a lot of questions which are answered in the documentation. This is not a problem, but simply reading through the manual (not the reference, the standard library docs, or the devdocs, just up to maybe Performance Tips from the Getting Started) may clarify a lot of things, then you can ask about the details).
Ok, I’ll investigate a bit before asking.