adibfara

public sealed interface Item permits Box, Container { }

adibfara

    public static void main(String[] args) {
        var ensemble = new Container(
                new Item[]{
                        new Box(2),
                        new Container(new Item[]{
                                new Box(3),
                                new Box(4)}
                        )});

        ensemble.visit(new PrinterVisitor());

adibfara

public interface ItemVisitor<T> {
    T visit(Box box);

    T visit(Container container);
}

public interface Item {
    <T> T visit(ItemVisitor<T> itemVisitor);
}

adibfara

public class WeightCalculator {
    public int calculate(Item item) {
        return switch (item) {
            case Box box -> calculate(box);
            case Container container -> calculate(container);
            default -> throw new IllegalStateException("Unexpected value: " + item);
        };
    }
    public int calculate(Box box) {
        return box.size();

adibfara

public record Box(int size) implements Item {}

public record Container(Item[] items) implements Item { }

adibfara

public interface Item {
    void printStructure();
    int weight();
}

adibfara

internal class ListedProcessor(
    private val environment: SymbolProcessorEnvironment,
) : SymbolProcessor {

    private fun Resolver.findAnnotations(
        kClass: KClass<*>,
    ) = getSymbolsWithAnnotation(
        kClass.qualifiedName.toString())
        .filterIsInstance<KSFunctionDeclaration>().filter {

adibfara

internal class ListedProcessor(
    private val environment: SymbolProcessorEnvironment,
) : SymbolProcessor {

    private fun Resolver.findAnnotations(
        kClass: KClass<*>,
    ) = getSymbolsWithAnnotation(
        kClass.qualifiedName.toString())
        .filterIsInstance<KSFunctionDeclaration>().filter {
            it.parameters.isEmpty()

adibfara

 // Inside your app's module, declare a dependency to your ksp module
 dependencies {
   implementation project(":ksp") // since you want to use your @Listed annotation
   ksp project(":ksp") // to make KSP work
 }

adibfara

// Create the directories: yourmodule/src/main/resources/META-INF/services/
// Create a file named com.google.devtools.ksp.processing.SymbolProcessorProvider
// Inside the file, add the following line (and nothing more):
com.snaky.ksp.processor.provider.ListedProcessorProvider

// For a reference, you can check out here:
// https://github.com/adibfara/ListGen/blob/main/ksp/src/main/resources/META-INF/services/com.google.devtools.ksp.processing.SymbolProcessorProvider