Kotlin will do exhaustive checks in a `when` block when it is an expression. You can add a `.let { }` at the end of the when statement if you want to enforce t

Kotlin will do exhaustive checks in a `when` block when it is an expression. You can add a `.let { }` at the end of the when statement if you want to enforce this and not really return anything. sealed class Communication data class Email(val emailAddress: String) : Communication() data class Shouting(val preferredName: String) : Communication() object HiveMind : Communication() fun exhaustiveWhen(comm: Communication) { // not exhaustively checked (will compile) when (comm) { is Email -> println("sending email to ${comm.emailAddress}") } // *is* exhaustively checked (error at compile time) // must add HiveMind or 'else' branch val result = when (comm) { is Email -> println("sending email to ${comm.emailAddress}") is Shouting -> println("HELLO, ${comm.preferredName}!") } // *is* exhaustively checked when (comm) { is Email -> println("sending email to ${comm.emailAddress}") is Shouting -> println("HELLO, ${comm.preferredName}!") }.let { } }