Kotlin Standard Library Cookbook

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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 ...