Did you watch Andreas's talk on ARC and ORC from Saturday's NimConf? He has a running example where he builds a toy `seq` from scratch, including the ref-counting.
Basically you can implement your own ref-counting, if your object is a non-`ref`. You give it a `ptr` to the shared state, and put a refcount in the shared state, and then implement the ARC hooks like `=destroy` and `=sink`.
