Kotlin Programming: The Big Nerd Ranch Guide, 2nd Edition

For the More Curious: Algebraic Data Types

Algebraic data types (or ADTs, for short) allow you to represent a closed set of possible subtypes that can be associated with a given type. Enum classes are a simple form of ADT.

Imagine a Student class that has three possible associated states, depending on the student’s enrollment status: NotEnrolled, Active, or Graduated.

Using the enum class that you learned about in this chapter, you could model the three states for the Student class as follows:

    enum class StudentStatus {
        NotEnrolled,
        Active,
        Graduated
    }

    class Student(var status: StudentStatus)

    fun main() {
        val student = Student(StudentStatus.NotEnrolled)
    }

And you could write a function that generates a student message using ...