Talk.kt

class Talk private constructor(id: String,
                               title: String,
                               duration: Duration) {

    val id = notBlank(id, "Cannot create a Talk is a blank id")!!
    val title = notBlank(title, "Cannot create a Talk is a blank title")!!
    val duration = notNegative(duration)
    val format = TalkFormat.ofDuration(duration)
}

TalkFormat.kt

enum class TalkFormat(val format: String, val durationRange: ClosedRange<Duration>) {
    IGNITE("IGNITE", ofMinutes(1).rangeTo(ofMinutes(10).minusNanos(1))),
    QUICKIE("QUICKIE", ofMinutes(10).rangeTo(ofMinutes(20).minusNanos(1))),
    TOOL_IN_ACTION("TOOL_IN_ACTION", ofMinutes(20).rangeTo(ofMinutes(40).minusNanos(1))),
    CONFERENCE("CONFERENCE", ofMinutes(40).rangeTo(ofMinutes(60).minusNanos(1))),
    UNIVERSITY("UNIVERSITY", ofHours(1).rangeTo(ofHours(4)));

    companion object Converter {
        fun ofDuration(duration: Duration): TalkFormat {
            isTrue(lessThanTheMinimumDuration(duration), "Duration is less than expected")
            return values()
                    .singleOrNull { duration.isInRange(it.durationRange) }
                    ?: UNIVERSITY
        }

        private fun lessThanTheMinimumDuration(duration: Duration): Boolean {
            val firstRange = IGNITE.durationRange
            return duration.coerceIn(firstRange) != firstRange.start
        }
    }
}