How can I iterate Dynamic object in Haxe

Question

I have Object parsed from JSON (haxe.Json.parse()) and I need to iterate over it. I already tried to cast this object to Array<Dynamic>:

var data:String='{"data":{"0":0,"1":1},"method":"test"}';
var res:{method:String,data:Array<Dynamic>} = haxe.Json.parse(data);
for (n in res.data)
    trace('aa')

There is no Can't iterate dynamic exception, just not working (iterating). I completley don't understand why in Haxe iterating procedure is so difficult.

This will only get you a list of field names. You'll also need to do Reflect.field(data, n); — Matthew Spencer, Mar 20 '13 at 21:13
@IgorBloom: I guess you forgot about this question. Out of courtesy, it would be nice to either accept an answer or comment what's wrong about them instead of leaving them in the open. Thanks. — dagnelies, Jun 24 '14 at 14:27
Sorry. Im starts using Reflects and its helps me in all ways — Igor Bloom, Aug 13 '14 at 18:31

Jason O'Neil · Accepted Answer · 2014-12-10T02:34:39.863

For the sake of posting a complete answer, and in case other people are wondering

In your first example, you've told the compiler that "res" contains two properties - one called "method" (which is a String) and one called "data" (which is Array). Now the JSON you're using doesn't actually have an Array<Dynamic>, it just has a dynamic object. An Array would look like: "data":[0,1].

So, assuming you meant for the JSON to have data as a Dynamic object, here is how you loop over it, using Reflect (as you mentioned in the comments):

var data:String='{"data":{"0":0,"1":1},"method":"test"}';
var res = haxe.Json.parse(data);
for (n in Reflect.fields(res.data))
    trace(Reflect.field(res.data, n));

Note here we don't have to specify the type of "res", since we're using Reflection just leaving it as Dynamic will be fine.

Now, if your JSON actually contains an Array, the code might look like this:

var data:String='{"data":[0,1],"method":"test"}';
var res:{method:String,data:Array<Int>} = haxe.Json.parse(data);
for (n in res.data)
    trace(n);

Here you use explicit typing to tell the compiler that res.data is an Array (and this time it actually is), and it can loop over it normally.

The reason you didn't get an error at compile-time is because the compiler thought there was genuinely going to be an array there, as you told it there was. At runtime, whether or not it throws an exception probably depends on the target... but you probably want to stay out of that anyway :)

Demo of both styles of code: http://try.haxe.org/#772A2

Jason, why are you so cool? :D You should write a book for Haxe! — Creative Magic, Jan 15 '14 at 09:19
in Haxe 3.1.3 (the current version) the array iteration gives the following compile error: `Test.hx:19: characters 11-19 : You can't iterate on a Dynamic value, please specify Iterator or Iterable` — anissen, Dec 09 '14 at 15:37
@anissen I've updated the try.haxe.org link to use the code in the answer here, and it works. The type annotation (`res:{method:String,data:Array}`) is necessary if you want to iterate. — Jason O'Neil, Dec 10 '14 at 02:35
Yeah, the book being a joint effort between Jason an @back2dos, it'd be awesome! — FullOfCaffeine, Jan 20 '18 at 20:02

How can I iterate Dynamic object in Haxe

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