Ordered dict by default

[Paul Rubin]

bearophileHUGS at lycos.com writes:
> Now Ruby dicts are ordered by default:
> http://www.igvita.com/2009/02/04/ruby-19-internals-ordered-hash/

Maybe I didn't read that carefully enough, but it looks like "ordered"
means the dict records come out in the same order you inserted them
in.  That is if you insert B,A,D,C in that order, you get them out in
that order.  I would have thought an ordered dict meant you get A,B,C,D,
which seems a lot more useful.

Red-black trees as described at the bottom of the page are a good way
to get A,B,C,D.  They also make it simple to have "persistent" or
"functional" dictionaries, which I've written about a few times before.