Once Arrow's code generation is configured, you can add the @lenses annotation to the data classes that you want to have lenses generated for:
import arrow.lenses
import arrow.optics.Lens
import arrow.optics.modify
typealias GB = Int
@lenses data class Memory(val size: GB)
@lenses data class MotherBoard(val brand: String, val memory: Memory)
@lenses data class Laptop(val price: Double, val motherBoard: MotherBoard)
fun main(args: Array<String>) {
val laptopX8 = Laptop(500.0, MotherBoard("X", Memory(8)))
val laptopMemorySize: Lens<Laptop, GB> = laptopMotherBoard() compose motherBoardMemory() compose memorySize()
val laptopX16 = laptopMemorySize.modify(laptopPrice().set(laptopX8, 780.0)) { size ->
size * 2
}
println("laptopX16 = $laptopX16")
}
Arrow generates as many lenses as constructor parameters our data classes have, with the name convention classProperty and in the same package, so no extra imports are needed.