Kotlin Metadata

Reflection.kt

package com.github.vmironov

import kotlin.reflect.jvm.internal.impl.serialization.ClassData
import kotlin.reflect.jvm.internal.impl.serialization.Flags
import kotlin.reflect.jvm.internal.impl.serialization.ProtoBuf
import kotlin.reflect.jvm.internal.impl.serialization.jvm.JvmProtoBufUtil

data class Foo(val foo: String)
data class Bar(val bar: String)

object FooFoo
object BarBar

fun main(args: Array<String>) {
  println("Foo is data? ${isDataClass(Foo::class.java)}")
  println("Bar is data? ${isDataClass(Bar::class.java)}")

  println("FooFoo is object? ${isObjectClass(FooFoo::class.java)}")
  println("BarBar is object? ${isObjectClass(FooFoo::class.java)}")
}

@Suppress("UNCHECKED_CAST")
fun getMetadata(target: Class<*>): ClassData? {
  val metadata = target.declaredAnnotations.singleOrNull {
    it.annotationClass.java.name == "kotlin.Metadata"
  } ?: return null

  val clazz = metadata.javaClass
  val d1 = clazz.getDeclaredMethod("d1").invoke(metadata) as? Array<String>
  val d2 = clazz.getDeclaredMethod("d2").invoke(metadata) as? Array<String>

  if (d1 == null || d2 == null) {
    return null
  }

  return JvmProtoBufUtil.readClassDataFrom(d1, d2)
}

fun isDataClass(target: Class<*>): Boolean {
  return getMetadata(target)?.let {
    Flags.IS_DATA.get(it.classProto.flags)
  } ?: false
}

fun isObjectClass(target: Class<*>): Boolean {
  return getMetadata(target)?.let {
    Flags.CLASS_KIND.get(it.classProto.flags) == ProtoBuf.Class.Kind.OBJECT
  } ?: false
}

fun isCompanionClass(target: Class<*>): Boolean {
  return getMetadata(target)?.let {
    Flags.CLASS_KIND.get(it.classProto.flags) == ProtoBuf.Class.Kind.COMPANION_OBJECT
  } ?: false
}