On 27.12.2010 15:18, Andreas Gal wrote:
Note that almost all implementations break for-in enumeration order for dense
arrays, for some definition of dense.
Example (firefox):
a = []
a[2] = 1
a[1] = 1
a[0] = 1
for (i in a) alert(i)
will alert 0, 1, 2 (in that order).
Now if you do
a["x"] = 1
you get 0, 1, 2, "x"
However, if we start out with x, we get this:
a = []
a["x"] = 1
a[2] = 1
a[1] = 1
a[0] = 1
Will alert x, 2, 1, 0
Hm, interesting (didn't know about SpiderMonkey), thanks.
Even worse, this is likely to change in the future (we want to give all objects
a dense, indexed part).
Most browser behave similar with respect to indexed properties. For good
performance you really want to ignore enumeration order for array-like objects,
but if the implementation falls back onto regular objects, you can suddenly
observe true property addition order.
Yep, indeed, with a = {} the order is as was specified in the source.
If we try to specify something, implementors will probably object, and each
implementation will have specific objections depending on their particular
array and object representation.
It's interesting. Could you summarize these objections?
Dmitry.
Andreas
On Dec 27, 2010, at 12:52 PM, Michael Day wrote:
Thanks Boris, Dmitry,
Are objects implicitly ordered, by implementation convention?
For implementations that have to deal with the web, yes.
Okay, now I know what we have to do then :)
Might I suggest that this be added to the spec, if only in an informative note,
to save future implementers the trouble?
Best regards,
Michael
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