There's more...

Range expressions can enhance use of the when expression as well. In the following example, we are going to implement a simple function that will be responsible for mapping a student's exam score to a corresponding grade. Let's say we have the following enum class model for student grades:

enum class Grade { A, B, C, D }

We can define a function that will map the exam score value, in the 0 to 100 % range, to the proper grade (A, B, C, or D) using a when expression, as follows:

fun computeGrade(score: Int): Grade =
        when (score) {
            in 90..100 -> Grade.A
            in 75 until 90 -> Grade.B
            in 60 until 75 -> Grade.C
            in 0 until 60 -> Grade.D
            else -> throw IllegalStateException("Wrong score value!")
        }

Using ranges together with the in operator makes the implementation of the computeGrade() function much cleaner and more natural than the classic equivalent implementation using traditional comparison operators, such as <, >, <=, and >=.