): Tags

  abstract operator fun <T : Any> get(key: KClass<T>): T?
}

/** An empty tags. This is always the tail of a [LinkedTags] chain. */
internal object EmptyTags : Tags() {
  override fun <T : Any> plus(
    key: KClass<T>,
    value: T?,
  ): Tags =
    when {
      value != null -> LinkedTags(key, value, this)
      else -> this
    }

  override fun <T : Any> get(key: KClass<T>): T? = null