On 27 Dec 2010, at 12:40, Andreas Gal wrote:
>
> I can't speak for other VM implementors, but I think most implementors will
> not want to guarantee either enumeration method (property addition order vs
> numeric order). In some cases we store array data "dense", in others we punt
> and use a natural object representation. The decision when we switch between
> representations is a brittle heuristics. Allowing the underlying
> representation and along with it the enumeration order to bleed through is
> faster than normalizing (which in some cases would mean sorting property
> indexed names).
>
> That having said, if TC39 decides to standardize enumeration order, I am
> pretty sure we can make pretty much any standard enumeration order reasonably
> fast (maybe a little less fast than before though). Mark suggested at some
> point enumerating indexed properties first in numeric order, and then all
> remaining properties. Its the most sensible approach I have heard so far. If
> someone drafts a proposal to standardize enumeration order, I volunteer to
> implement it in Firefox and get some performance data. That would help
> calming implementor's nerves.
>
> Andreas
As an interesting related tidbit: ruby 1.9 changed the key order on its hashes
from sorted to insertion order:
http://www.markhneedham.com/blog/2010/09/07/ruby-hash-ordering/
http://www.igvita.com/2009/02/04/ruby-19-internals-ordered-hash/
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