yup, basically the struct instance is an integer... but you cannot directly use it effectively... because allocation of structs are a bit random from my experience.
example: I have missile spells, then I added debug messages which gave me the instance of each missile created, it gives something like, [1,2,3,5] or [1,4,2,10] so its pretty hard to use the instances as an index directly... well you can loop from 1-8190 but it would be inefficient...
so we use an indexing system instead to loop only the in-use struct instances.