data class Vehicle {
    val name: String,
    val type: VehicleType,
    val fuel: FuelType
} {
    init {
        validate(this) {
             validate(Vehicle::fuel)
                 .isNotEqualTo(FuelType.DIESEL)
                 .when { it.type is VehicleType.TWO_WHEELER}
        }
    }
}

 data class Vehicle(
        val name: String,
        val type: VehicleType,       // VehicleType is either TWO_WHEELER or FOUR_WHEELER
        val fuel: FuelType              // FuelType is either PETROL or DIESEL
    )

//    declare function that returns the function which returns Boolean
    val bikeEngineValidation: (type: VehicleType) -> (fuel: FuelType) -> Boolean = { vehicle ->
        { fuel ->
            !(vehicle == VehicleType.TWO_WHEELER && fuel == FuelType.DIESEL)
        }
    }

//    invalid bike
    val bike = Vehicle("bike", VehicleType.TWO_WHEELER, FuelType.DIESEL)
    try {
        validate(bike) { vehicle ->
            validate(Vehicle::fuel).isValid { bikeEngineValidation(vehicle.type)(it) }
        }
    } catch (ex: ConstraintViolationException) {
        ex.constraintViolations
            .map { "got validation error -> ${it.property}: ${it.constraint.name}" }
            .forEach(::println)
    }