Exhaustive

Denote a when statement which is required to exhaustively cover all cases.

The Kotlin compiler will only enforce exhaustiveness for a when used as an expression. This annotation extends that same enforcement to statement whens. Additionally, these whens are forbidden from having an else branch since it is mutually exclusive with exhaustiveness.

enum class RouletteColor { Red, Black, Green }

fun printColor(color: RouletteColor) {
  @Exhaustive
  when (subject) {
    Red -> println("red")
    Black -> println("black")
  }
}

Compilation of the above will fail with:

e: Example.kt:5: @Exhaustive when is not exhaustive!

Missing branches:
- RouletteColor.Green

Constructors