You can define and derive from any abstract class you define, as long as any of your superclasses is a Godot class.

This allows you to define default functions for your inheriting classes and override them in some, but not all subclasses if you want.

You can define a abstract class and register it's members the same way as you do for normal classes.

Under the hood, we only register your normal classes, and let them register all members your abstract class defines.

Info

For this reason, the @Script annotation is optional for abstract classes.

Warning

As in Kotlin, you cannot instantiate abstract classes directly from any other scripting language like GDScript! In fact, godot does not even know (or care) that your abstract class exists.

Example

Abstract class definition:

// register class annotation is optional for abstract classes
abstract class AbstractClassInheritanceParent: Node() {

    @Export
    var registeredExportedPropertyInAbstractClass = false

    @Emit("blubb")
    val signalInAbstractClass by signal<String>()

    @Register
    fun functionInAbstractClassWithDefaultImplementation() {
        // some implementation
    }

    @Register
    abstract fun abstractFunction()
}

Child class definition:

@Script
class AbstractClassInheritanceChild: AbstractClassInheritanceParent() {
    override fun abstractFunction() {
        // some implementation
    }
}

Overridden members

Overriding a parent member changes its behavior. If the child should also be exposed differently, add the annotation again on the child declaration.