Learn Haxe

Deserializing Class Instances From Json

Posted on 2016-03-22

Tagged with: Haxe

If you google for how to deserialize some JSON into a Haxe class, you will most likely find this API page on JSON parsing.

While this method allows you to deserialize JSON into a struct, it only works with a typedef. It won't work with an actual class (something that has methods).

The good news is that it is possible to deserialize to a class instance; the bad news is that it relies on reflection. The snippet below uses reflection to iterate over all fields in the dynamic instance returned by haxe.json.parse, and reflectively sets the values on myInstance:

var raw = haxe.Json.parse(sys.io.File.getContent(configFile));
var myInstance:WhateverClassYouWant = new WhateverClassYouWant();

var structsFields:Array<String> = Reflect.fields(raw);
var classFields:Array<String> = Type.getInstanceFields(Type.getClass(myInstance));

for (field in structsFields)
{
    if (classFields.indexOf(field) > -1)
    {
        var value:Dynamic = Reflect.field(raw, field);
        Reflect.setField(myInstance, field, value);
    }
}

A couple of caveats to pay attention to:

• We only set the field on myInstance if it exists. This is safer than trusting the JSON blindly.
• Any fields that aren't in raw (or in the JSON) won't be set, and will have their default values.

As it stands, this solution can work pretty well as a class deserializer. You can use a similar method to reflect and serialize a class to JSON.