MobileDev: Kotlin-Workshop — student after

Main.kt

fun main() {
    val john = Student(age = 18, name = "John Doe")
    john.age = john.age + 1
    println("${john.name}, ${john.age}, ${john.age.ageGroup}")

    val card = StudentCard(123, john)
    println("$john, $card")

    val students = List(5) { index -> Student("Student", index) }
        .map { StudentCard(it.age, it) }
        .filterIndexed { index, _ -> index % 2 == 0 }
        .drop(1)
    println(students)
}

/**
 * _This_ `class` represents a __single__ [Student].
 */
class Student(
    val name: String,
    age: Int = 19
) {
    var age: Int = age
        set(value) {
            require(value > age) { "age must increase" }
            field = value
        }
}

data class StudentCard(
    val id: Int,
    val student: Student
)

val Int.ageGroup: String
    get() = when (this) {
        in 0 until 13 -> "Child"
        13 -> "Sad life"
        in 14 until 20 -> "Teenager"
        else -> "Adult"
    }