[Flash] Type coercion failure when loading maps from SharedObject

[Oxdeception]

Describe the bug
Type coercion fails when attempting to use a map loaded from a SharedObject in the Flash target.

Steps to Reproduce

1. Save a Map in a SharedObject
2. Load SharedObject
3. Attempt to use saved Map

Minimal Example

import openfl.events.Event;
import openfl.events.MouseEvent;
import openfl.net.SharedObject;
import openfl.display.Sprite;

class Main extends Sprite {
    var myMap:Map<String, Int> = ["test" => 1];
    public function new () {
        super();
        this.addEventListener(Event.ADDED_TO_STAGE, setup);
    }

    public function setup(e:Event) {
        this.stage.addEventListener(MouseEvent.CLICK, save);
        this.stage.addEventListener(MouseEvent.RIGHT_CLICK, load);
    }

    function save(e:Event) {
        var save = SharedObject.getLocal("test", "/");
        save.data.myMap = myMap;
        save.flush();
        trace("Saved");
    }

    function load(e:Event) {
        var load = SharedObject.getLocal("test", "/");
        trace(Type.getClassName(Type.getClass(load.data.myMap)));
        myMap = load.data.myMap;
        trace("Loaded");
    }
}

Expected behavior
Map is loaded from the SharedObject

Screenshots

TypeError: Error #1034: Type Coercion failed: cannot convert Object@2800c5302e51 to haxe.IMap.
        at Main/load()[/Projects/Haxe/issues/SharedObjectMaps/Source/Main.hx:28]

OpenFL Targets
Flash

Additional context
Does not occur on other targets.

[joshtynjala]

With SharedObject and ByteArray, only the core AS3 language types can be serialized automatically. As I understand it, custom types need to implement flash.utils.IExternalizable to be restored when read from a SharedObject or a ByteArray (and i think maybe flash.net.registerClassAlias needs to be involved too).

Since haxe.IMap does not implement the IExternalizable interface, and we can't force it to implement that interface because it's a Haxe core language type that isn't under OpenFL's control, there probably isn't much that can be done to improve this situation. You may want to consider using a different type that can be serialized. For instance, Flash's Dictionary type is relatively similar to Map (though it isn't strictly typed like Map, so it's not a perfect replacement).

It may also be possible to create a custom IMap implementation that also implements IExternalizable. It could use a regular Map internally to store the data, and act as kind of a wrapper. I've never tried this myself, but it might be something to look into, if you really want to use a map, and would prefer to avoid another type.