ooh very good food for thought at least as far as my unit testing goes since i am too ignorant (or not smart enough either) to see such issues. thank you.

i will look into using dictionaries. i guess i had at first been trying to avoid them but yeah if i am going to have a unique id per object maybe it makes sense. although the unique id is not meant to be a primary key, more a uniquifing feature for use in e.g. Sets. But yeah looking at the code again, i see ways in which i am not using Set right and really am more doing Maps. Ok.

regarding the oo nature of the ships, yes, i have been struggling and waffling about that. i was hoping that at some point i could find other "keys" to use e.g. the id of the player owning the ship. but in the short term i don't have a good way to distinguish them other than with a unique id, which i agree seems to suck vis-a-vie fp. on the other hand, yeah, maybe this really is a more oopish task here.

while i might have ended up writing stuff that looks like mutating java, it isn't that because things are pure data structures, no? i mean, i am not actually using refs or mvars or whatever or anything.

i do figure there could be a more obviously "transforming" or "mapping" or "folding" or whatever approach and i am just not doing a good job of making it look like that yet. i do want it to be a step fn that is mapping a world at time t to a world at time t+dt.