Kotlin: Return can be lifted out of 'when'

Question

The alternative to switch in Kotlin is when. So, inside a recycler view adapter, when I am returning view type, I use when:

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

But, the above statement sends our warning message Return can be lifted out of 'when'.

Does anyone know what may be the correct way of using when? And what should be done to fix the above case?

Answer 1

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 }