matz / ruby-lang.org (Yukihiro Matsumoto) writes:

[...]

> |How hard would it be to have an option to use reference counting in a
> |particular class?
> 
> It must be pretty hard under the current implementation.  The garbage
> collector sits in the middle of the core.  I'm now investigating
> partial reference count (maybe 1bit refcounting) for Rite.  It should
> provide you immediate object finalization (if you're lucky) and thread
> safety.

for completeness the other solution is region inference: 
  replace most (in some programs, all) of the need of GC by stack-based memory
  management
  http://citeseer.nj.nec.com/tofte98region.html