NumberListAdapter.kt

class NumberListAdapter : ListAdapter<Int, ViewHolder>(object : DiffUtil.ItemCallback<Int>() {
  override fun areItemsTheSame(oldItem: Int?, newItem: Int?) =
      oldItem == newItem // check uniqueness

  override fun areContentsTheSame(oldItem: Int?, newItem: Int?) =
      oldItem ==  newItem // check contents
}) {

  ...                             
}