Append does not work on Polygon2D.polygon

[zln_0]

Godot Version

4.2.1

Question

I have a simple program that spawns a single Polygon2D.
I can substitute Polygon2D.polygon for a PackedVector2Array, but I cannot append a vertex. Since substituting it for a different PackedVector2Array works, it does not seem to be immutable after the first assignment.
Why is this and where can I get information about things like this? (I am new to this)
(edited for better readability)

extends Node2D


# Called when the node enters the scene tree for the first time.
func _ready():
	var polygon = Polygon2D.new()
	var points = PackedVector2Array()
	points.append(Vector2(0,0))
	points.append(Vector2(100,0))
	points.append(Vector2(100,100))

	var points2 = PackedVector2Array([Vector2(420,200),Vector2(0,300),Vector2(0,0)])

	polygon.polygon = points
	print(polygon.polygon) # [(0, 0), (100, 0), (100, 100)]

	polygon.polygon.append(Vector2(200,280)) # this does not seem to do anything
	print(polygon.polygon) # [(0, 0), (100, 0), (100, 100)]

	polygon.polygon=points2
	print(polygon.polygon) # [(420, 200), (0, 300), (0, 0)]

	polygon.offset = Vector2(100,100)
	polygon.color = Color(1,1,1)
	add_child(polygon)
	
	pass # Replace with function body.


# Called every frame. 'delta' is the elapsed time since the previous frame.
func _process(delta):
	pass

[smix8]

You need to run the setter for all the node update logic and (re)assigning an array runs the setter. Doing just internal changes to an array does not notify anything.

[zln_0]

how do you update without performing an assignment? there are no such methods in the documentation for Polygon2D. do I call something like get_bone_count?
Also, when using print after appending on Polygon2D.polygon, I got the PackedVector2Array before the append, so I am not sure it is just the Polygon2D not acknowledging the update.

[smix8]

PackedXYZArrays are copy-on-write. If you do any changes to them you create a copy.