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Iterate Over all Fields of Anonymous Structures in Haxe

Posted on 2016-02-17

Tagged with: Haxe

How do you iterate over all fields of an anonymous structure (possibly behind a typedef) in Haxe and print out all the values?

The Haxe reflection docs suggest:

The reflection API consists of two classes: - Reflect: A lightweight API which work best on anonymous structures, with limited support for classes. - Type: A more robust API for working with classes and enums.

Reflect seems promising. From perusing the API docs, I noticed a fields method. The docs say:

static fields (o:Dynamic):Array

Returns the fields of structure o.

This method is only guaranteed to work on anonymous structures. Refer to Type.getInstanceFields for a function supporting class instances.

That looks promising. Running Reflect.fields({ "name": "Butterfly", "version": "0.3" }) gives me the array ["name", "version"] back.

Reflect also includes a getProperty method, which returns the value of a property. Plug this into a for-loop, like so:

var target = { "name": "Butterfly", "version": "0.3" };
var fields = Reflect.fields(target);
for (field in fields) {
  var value = Reflect.getProperty(target, field);
  trace('${field} => ${value}');
}

This traces:

name => Butterfly version => 0.3

Also, note that Reflect also contains a field method which is syntactically similar to getProperty (same inputs and outputs); the difference is that field ignores accessors, while getProperty applies accessors.

Given the choice, in this specific case of anonymous structures, I would use field instead of getProperty for readability. This:

for (var field in Reflect.fields(target)) { Reflect.field(...) }

Reads more sensibly than:

for (var field in Reflect.fields(target)) { Reflect.getProperty(...) }

If you apply this on something other than an anonymous structure, you should probably opt for getProperty instead.