Comments on: AS3 for…in Object does not behave like AS2

By: Joe Wheeler

Joe Wheeler — Mon, 23 Feb 2009 13:42:47 +0000

Actually even in AS2 the order of iteration of a for…in loop is unpredictable. Try using it on a sorted Array and you'll see what I mean. Check the documentation too, it's mentioned in there.

By: Steve Kamerman

Steve Kamerman — Wed, 02 Jul 2008 19:40:57 +0000

To get a similar effect in AS3 you need to use an Array of objects, like this:

var data:Array = [
{a: 1},
{b: 2},
{c: 3}
];

for (var i:uint=0;i var obj:Object = data[i];
var s:String;
for(s in obj){break;} //set s

trace(s + " = " + obj[s]);
}

By: calvin

calvin — Tue, 24 Jun 2008 18:50:49 +0000

I agree that the main problem in as3 is the fact that you can only iterate over genuine Object objects…
Even casting to Object doesnt work..so there is a LOSS of functionality here. I wish I knew a workround this was quite an elegant way of doing something which now I see no solution but to engineer a specific array or other.

By: Philip Thonbo

Philip Thonbo — Fri, 30 May 2008 14:37:26 +0000

what about the fact that you in as2 could use displayObjects(movieclips) and whatever to run a for(i in this)
on. and it would return EVERYTHING incl [type Function] script objects visible objects everything – you could trace a mc.filters[0] to get vars from a filter object created in flash ide – [object BlurFilter] now you can ONLY iterate through an strict Object object – it is so lame tell me if you find any work around on THAT

By: corban baxter

corban baxter — Fri, 11 Apr 2008 16:27:31 +0000

its things like this that make me want to never be a "REAL" programmer!

By: Mike Keesey

Mike Keesey — Mon, 07 Apr 2008 23:33:37 +0000

If your code relies on order, you should not be using for … in, anyway. The language's "contract", so to speak, does not guarantee any particular order.

Java's collections make the distinction a little more explicit: most Collection objects don't guarantee any order, but the List subinterface does.

By: michal

michal — Mon, 07 Apr 2008 22:57:38 +0000

My guess would be that the implementation uses a hash table for both object properties and the Dictionary. This would guarantee fast O(1) inserts/searches but do not provide any reasonable ordering which is exactly what you're seeing.
The alternative is a tree set which would provide alphabetical ordering of keys at the cost of slower O(log(n)) inserts/searches.
I'm not sure what tests you did in Java as it gives you explicit choice of HashMap and TreeMap depending on your needs.
The rule of thumb I was taught: unless you need the ordering use the hash set asd it's faster. So they did in AS3 I guess.
I'm trying to think how you'd get first in/first out ordering on a dictionary and I can only come up with a list of key/value pairs which is extremely inefficient for anything other than inserts.