Enumeration in kotlin

enums.kt

package enumerations


fun main() {
    val east = Direction.EAST
    println(east.notation)
    println(east.oppositeDirection())

    //println(east.opposite()) // not possible, you cannot invoke extension function declared inside class
    east.westOpposite()
}
enum class Direction(val notation: Char) {
    EAST('E'),
    WEST('W'),
    NORTH('N'),
    SOUTH('S');


    // declaring extension function inside enum class.
    // we cannot invoke this function outside the class at all
    fun Direction.opposite() =
        when(this) {
            EAST -> WEST
            WEST -> EAST
            NORTH -> SOUTH
            SOUTH -> NORTH
        }


    fun westOpposite() {
        println(WEST.opposite())
    }
}


fun Direction.oppositeDirection() =
    when(this) {
        Direction.EAST -> Direction.WEST
        Direction.WEST -> Direction.EAST
        Direction.NORTH -> Direction.SOUTH
        Direction.SOUTH -> Direction.NORTH
    }