Add support for class inheritance between separate GDExtensions

[CsloudX]

Describe the project you are working on

No-Game APP

Describe the problem or limitation you are having in your project

I want create a base class DeviceBase in DeviceBase plugin.
and then create a sub class DeviceA in DeviceA plugin.
and then create a sub class DeviceB in DeviceB plugin.

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

I'm test much work with visual studio, and all failed.

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

none

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

I want gdextension c++ support this.

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

it should be core.

[dalexeev]

Note that different gdextensions can be implemented in different languages. Each language has its own specifics. For example, statically typed languages ​​typically require the source code for dependencies to be available at compile time, or at least the header files to know the class interface.

Most languages ​​cannot easily inherit classes or even use code from other programming languages ​​(there are a few exceptions where languages ​​allow the use of C header files directly, but usually, you can only call an extern C function).

I'm not saying this is impossible in principle, but it is very difficult and largely depends on language bindings. Each supported language must be able to generate the necessary information (such as source code) to construct the base class interface based on its exposed information for Godot. See also the proposal #12155. Theoretically, this would make it possible to inherit from a class written in another language or contained in another extension. It would also require some kind of Godot package manager.

Please note that you can currently use Godot's dynamic capabilities to interoperate between different scripting languages ​​and gdextensions (but you still cannot inherit from other classes):

• You can verify that the required extension is loaded using the GDExtensionManager API.
• You can get a list of classes and other information about them, instantiate a class, etc. using the ClassDB API.
• You can access object properties, call methods, connect/disconnect signals, etc. using the Object API.

[dsnopek]

Allowing a class in one extension to extend a class from another extension is something I've spent quite a bit of time looking into, and I would like to implement it eventually!

In fact, I think it will quite important after C# moves to GDExtension, because otherwise C# classes won't be able to extend classes from GDExtension like they can now (and the API of some GDExtensions requires making a child class)

That said, there really is a lot involved in making this work. We'll need to:

• Make quite a few changes to the GDExtension interface
• Allow GDExtensions to list dependencies (and for Godot to load them in the appropriate order based on those dependencies)
• Allow Godot to create an extension_api.json with data from only a particular GDExtension (or set of extensions?)
• Update the godot-cpp (and other bindings) to "merge" multiple extension_api.jsons when generating code (along with updating it for the afformentioned GDExtension interface changes)

And that's not even digging into the "package management" question, which I haven't thought about at all - I've only been looking at how to make it work at a low level

So, I agree that we should do it, but it could take awhile :-)