Type of a scene with script attached

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1

Godot Version

4.3 beta 2

Question

Hey there, good people.

I’m new to Godot, but not to programming. Right now, I’m learning Godot with GDScript, but I plan on eventually programming in C++ using GDExtension.

I had a problem downcasting a 2DNode scene instantiated to the type declared in the attached script (using the as keyword). In a dynamically typed language, this is less of a problem since you can call the methods anyway, but what about statically typed languages like C# and C++, what happens there?

I saw in the scene type menu you have “extends,” but I couldn’t find the class in the script. Maybe I’m missing something.

Can you downcast the scene to the associated class in C# and C++?

If we can in statically typed languages, should we have a request to have it also in GDScript? I’m not sure it’s a high priority, though.

I just want to say that I’m grateful for the existence of this full-fledged open source game engine. It’s awesome!

2

You don’t needed downcast, you have Access to all public methods and variables of parent class

3

Each script (in gdscript) is a class.

What trouble did you have with casting?

4

@dbat, I realise that the script is a class, that’s why I was supprised I couldn’t downcast to that class.

classname Card # without this I get a compile error
.
.
.
var c = _card_packed.instantiate();
add_child(c)
var type_name = c.get_class() # returns "Node2D"
var card: Card = c as Card # <--- fails, card is being set to null

@Moreus I already wrote in the question that due to the dynamically typed nature of GDScirpt, I can treat it like the derived class. There is an effort to make GDScript optionally typesafe; hopefully one day there will be a “strict typing” checkbox option in the setting that forces you into putting types on every variable.
Also without downcasting I’m loosing the ability to get “intellisense” completions.

5

Welcome to the club. Sadly, for no reason I can fathom, classes we write in gdscript are not delivered via methods like get_class.

Checkout my short write-up here for some ideas: Class Hacks in Godot · Wiki · Donn Ingle —Dbat / lessons-in-dev · GitLab

At the moment there is a big bug-fix on to just get Godot to respect the class_name keyword in the first place, without a million startup errors every time.

It’s a process.

2 Likes
6

So it is a GDSCript specific issue, not affecting C# and C++, right?

7

Afaik. But test yourself.

8

Can you post both the exact code you wrote and what you are trying to achieve?

This code works as expected if the _card_packed root node has the Card script attached and the Card script is free of parse errors.

Side notes:

  • get_class() is to get the engine built-in type.
  • The script class “name” is effectively the path to the script resource. The script “type” is effectively the instance of the Script object.
  • Use the is operator to test script or built-in object types.
  • Inheritance works as expected in C++ and C#. In C++, you should use Object::cast_to<T>().
  • You cannot cast your C++ objects to GDScript types. You can set_script() of C++ objects and delegate to the assigned script.
1 Like
9

Perhaps you can write “class_name YourClass” at the beginning of the script of the class you need after “extends YourClassNode”, then you can immediately create it in the “add node” function in the hierarchy and maybe this will help with your problem. It’s not a fact that it will work. Just a guess.
Sample code:
extends Node2D

class_name MyClass

var t
vat y

func _ready()
pass

10

The packedscene does have the card script attached to it. It even shows when I inspect the return value from c.get_script().
Thanks, @indicainkwell, the side notes are really useful info. I guess I
can also create a pseudo abstract class in c++, with the interface to be implemented in the gdscript, and use it as the base class for the gdscript node, if I really wanted to.