I am not sure I understood correctly. Any `ref`-ed object on the heap is garbage-collected. So if your Nim library, called by Java, internally makes use of them, then you get garbage collection "for free".
The only thing I am not sure of is whether or not one can access `ref` objects from another language. If so (which is currently unlikely as hinted in the documentation), I have no idea of how these would be handled...
