How does the property list work?

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1

Godot Version

4.3

Question

I’m trying to write a GDExtension that exposes a Component class that inherits from Object. The intention is that in GScript the user will inherit Component and add their own data to it.

What I want is a function that returns the list of user added non-function properties and the size of them. So far if I print the property list of a class that inherits Component from C++ then the property list is empty.

If I call get_properties_list() directly from GDScript then I get the additional types that are added to the class, but I also get several additional properties script or built-in-script.

So rather than ask for a solution, I am hoping that someone can explain the propety list system to me so that I can write a proper solution that does what I want.

1 Like
2

I’m a bit confused what you are trying to do, but you can use the class keyword to create objects that inherit from object.

E.g.
test.gd

class_name Test

class Result:
	var code: int=0   # Error Code
	var description: String="" # Error Message
	var value: Variant # Value if no error

	func print_me():
		print(self.description)

static func get_props(the_class:Variant) -> Dictionary:
	var props={}
	var flags=PROPERTY_USAGE_SCRIPT_VARIABLE
	for prop in the_class.get_property_list():
		if(prop.usage & flags>0):
			props[prop.name]=the_class.get(prop.name)
	return props

some script that uses classes inside test.gd

extends Node2D

func _ready():
	var res:Object=Test.Result.new()
	res.code=-1
	res.description="Error"
	res.value=null
	print(Test.get_props(res))
	res.print_me()
3

Sorry, I don’t think I explained it quite well. What I am trying to do is have a base class that has a function that only returns the data properties in the classes that derive from it.

E.g.:

// in .cpp

class Base : public Node { 
    /* Godot boiler plate */

   PropertyList get_property_list() // <-- returns the data types stored in a derived class
}

And then in Godot you would have something like:

class_name Derived extends Base

var code: int=0   # Error Code
var description: String="" # Error Message
var value: Variant # Value if no error

extends Node

func _ready():
    var test: Derived = Derived.new()
    
    var properties = test.get_property_list()
    for property in properties:
        print(property)

Which would end up printing something along the lines of :

"code" : Int
"description": String
"value": Variant

But doesn’t include the additional properies like script or built-in-script etc.