Add support for multiple individual named classes in the same script file (Gdscript)

[izzyn]

Add support for multiple individual named classes in the same script file (Gdscript)

Description

Add support to have multiple independent named classes in the same file. I.A Defining two classes within the same file, then being able to reference those classes completely independently as if they were defined in two different files.

Describe the project you are working on

I am working on a map painting game with heavily abstracted logic for events, popups, buildings and alike (for future mod support). I propose this feature as it would be really helpful for me when I write different implementations of some type of resource. For example, I have a "condition" class that is used to validate different types of conditions within the game, which has different subclasses for different implementations of the conditions class (an AND condition, a resource check condition etc.)

Describe the problem or limitation you are having in your project

Sometimes you have really small classes, or a collection of implementations that are different enough to warrant being different classes, but similar enough that it would be more readable to have them all in one file. It's also quite annoying to navigate a project that necessitates having so many files (even with a neat folder structure).

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Add syntax for defining different classes within the same file. A way to do this would be to define multiple "extends X class_name Y" below eachother to signify different classes.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

(This obviously depends on how the team wants to implement the feature)

# Implementation 1
extends Superclass
class_name Subclass_A

var A = 10
func fetch_var(): return A 
   pass

# Implementation 2
extends Superclass
class_name Subclass_B

var B = -200
func fetch_var(): return B
   pass

Then in another file

func some_logic():
 var A = new Subclass_A()
 # Prints 10
 print(A.fetch_var())
 var B = new Subclass_B()
 # Prints -200
 print(B.fetch_var())
 pass

If this enhancement will not be used often, can it be worked around with a few lines of script?

Personally, I think it is used often. But if it isn't you can create a superclass in the file, and then add a bunch of subclasses within that superclass, this isn't nice however, since you would have to refer to that superclass when you want to create instances of the subclasses and that should be unnecessary.

Is there a reason why this should be core and not an add-on in the asset library?

It adds fundamental syntax to the gdscript language, so I think it fits as a core feature.

[sockeye-d]

Since one script represents one class, it's easy to determine the type of a node when a script is attached. What happens when you attach a multi class script to a node? How will it know which class's functionality to assign to the node?

[izzyn]

Since one script represents one class, it's easy to determine the type of a node when a script is attached. What happens when you attach a multi class script to a node? How will it know which class's functionality to assign to the node?

This is true! I was mainly considering resources in this case. So I have no real answer for that.

[izzyn]

Oh and also you can already create subclasses with the class keyword, although subclasses are not assignable to a node

Yes, but as far as I am aware, those classes are not accessible outside of that one file. Which is a really arbitrary limitation IMO. (This is because in my testing, you have to use the class_name field in order to create a proper class in the sense that it's inheritable and creatable by other scripts)

[sockeye-d]

You can access subclasses from the parent script like another property access. Like this:

class_name MyClass

class SubClass:
    static func my_function() -> int:
        return 48

# elsewhere...
print(MyClass.SubClass.my_function()) # 42

[sockeye-d]

I was mainly considering resources in this case

Even with this, the custom resources are just a normal resource with a script attached so you'll have the same issues

[izzyn]

You can access subclasses from the parent script like another property access. Like this:

class_name MyClass

class SubClass:
    static func my_function() -> int:
        return 48

# elsewhere...
print(MyClass.SubClass.my_function()) # 42

I mention this in my post. "You can create a superclass in the file, and then add a bunch of subclasses within that superclass, this isn't nice however, since you would have to refer to that superclass when you want to create instances of the subclasses and that should be unnecessary."