I didn't finish this sentence:

On Fri, Sep 25, 2009 at 7:34 PM, Charles Oliver Nutter
<headius / headius.com> wrote:
> JRuby and IronRuby. But if Enumerator#next were predicated on a
> collection implementing both each and to_enum.

But if Enumerator#next required you to implement to_enum, people
writing new collections could opt into cursor-based enumeration in a
more cross-compatible way. Ideally a custom to_enum impl would return
a lightweight enumerator with a simple position, but a library author
could implement it in other ways that don't require fibers or threads.

- Charlie