Sealed hierarchies versus enums

In Kotlin, while enums are suitable for a fixed set of constants, sealed interfaces and classes provide a more flexible and powerful alternative, especially when dealing with a state machine-like scenario or when additional data needs to be associated with each state.

In Java, enums are often used to represent a fixed set of states and can be overloaded with functionality. Consider a pizza order tracking system:

enum class PizzaOrderStatus {
    ORDER_RECEIVED, PIZZA_BEING_MADE, OUT_FOR_DELIVERY, COMPLETED;
 
    fun nextStatus(): PizzaOrderStatus {
        return when (this) {
            ORDER_RECEIVED -> PIZZA_BEING_MADE
            PIZZA_BEING_MADE -> OUT_FOR_DELIVERY
            OUT_FOR_DELIVERY -> COMPLETED
            COMPLETED -> COMPLETED
        }
    }
}

This approach is straightforward but limited in terms of scalability and flexibility.

Sealed interfaces in Kotlin allow for a more expressive representation of...