Kotlin: Return can be lifted out of 'when'

You’re using when like a simple Java switch statement, which is okay but not very idiomatic and can be improved. You can refactor your code in two steps:

1. Kotlin's when can be used as an expression, it returns a value if you wish:

   override fun getItemViewType(position: Int): Int {
       return when (position) {
           0 -> ItemViewType.TITLE.type
           1 -> ItemViewType.SUBTITLE.type
           2 -> ItemViewType.ITEM.type
           else -> -1
        }
   }
   

2. The function body, now consisting of a single statement, can be changed into an expression body:

   override fun getItemViewType(position: Int) = when (position) {
        0 -> ItemViewType.TITLE.type
        1 -> ItemViewType.SUBTITLE.type
        2 -> ItemViewType.ITEM.type
        else -> -1
   }
   

Your when is correct, however Kotlin has the ability to lift the return out of the 'when' if you are returning in every case, thus it becomes :

override fun getItemViewType(position: Int): Int {
    return when (position) {
        0 -> ItemViewType.TITLE.type
        1 -> ItemViewType.SUBTITLE.type
        2 -> ItemViewType.ITEM.type
        else -> -1
    }
}