Simple implementation of Distance in Kotlin

Distance.kt

@JvmInline
value class Distance internal constructor(private val rawValue: Long) : Comparable<Distance> {
    override fun compareTo(other: Distance) = this.rawValue.compareTo(other.rawValue)

    val inWholeMeters: Long
        get() = toLong(DistanceUnit.METERS)

    val inWholeKilometers: Long
        get() = toLong(DistanceUnit.KILOMETERS)

    operator fun plus(other: Distance) = Distance(rawValue + other.rawValue)
    operator fun minus(other: Distance) = Distance(rawValue - other.rawValue)

    private fun toLong(targetUnit: DistanceUnit) = convertDurationUnit(rawValue.toDouble(), DistanceUnit.MILLIMETERS, targetUnit)

    companion object {
        val ZERO: Distance = Distance(0L)

        inline val Long.meters get() = toDistance(DistanceUnit.METERS)
        inline val Long.kilometers get() = toDistance(DistanceUnit.KILOMETERS)
        inline val Int.meters get() = toDistance(DistanceUnit.METERS)
        inline val Int.kilometers get() = toDistance(DistanceUnit.KILOMETERS)
        inline val Double.kilometers get() = toDistance(DistanceUnit.KILOMETERS)
    }
}

fun Long.toDistance(unit: DistanceUnit): Distance {
    val inMillimeters = convertDurationUnit(this.toDouble(), unit, DistanceUnit.MILLIMETERS)
    return Distance(inMillimeters)
}

fun Double.toDistance(unit: DistanceUnit): Distance {
    val inMillimeters = convertDurationUnit(this, unit, DistanceUnit.MILLIMETERS)
    return Distance(inMillimeters)
}

fun Int.toDistance(unit: DistanceUnit): Distance {
    val inMillimeters = convertDurationUnit(this.toDouble(), unit, DistanceUnit.MILLIMETERS)
    return Distance(inMillimeters)
}

private fun convertDurationUnit(value: Double, unit: DistanceUnit, target: DistanceUnit) =
    unit.convert(value, target)