Kotlin and ADT

"We'll talk about what algebraic data types are and how you can start using them today. We are not going to dive into any frameworks, so it does not matter whether you are a frontend or backend developer - it will be equally useful."
by Dmitry Zaytsev
presented on August 22, 2017 at @car2go

Transcript

1. Hey! Here is Dmitry Zaytsev from car2go 1 / 37
2. Kotlin + ADT = ❤ 2 / 37
3. What is an ADT? For those who don't have PhD 3 / 37
4. What is an ADT? Algebraic Data Type 4 / 37
5. What is an ADT? Algebraic Data Type Type which is represented by several other types 5 / 37
6. enum OperationStatus { SUCCESS, FAILURE, IN_PROGRESS } 6 / 37
7. Hey, that's Java! 7 / 37
8. What is an ADT? Algebraic Data Type Type which is represented by several other types enum is also an ADT 8 / 37
9. Let's get real 9 / 37
10. class OperationStatus<T> { public final Stage stage; public final T result; public final String errorMessage; enum Stage { SUCCESS, FAILURE, IN_PROGRESS } } 10 / 37
11. Problems with that Not clear what this operation represents 11 / 37
12. Problems with that Not clear what this operation represents Fields are null depending on stage 12 / 37
13. class OperationStatus<T> { public final Stage stage; public final T result; public final String errorMessage; enum Stage { SUCCESS, FAILURE, IN_PROGRESS } } 13 / 37
14. Kotlin to the rescue! 14 / 37
15. sealed class OperationStatus<T> 15 / 37
16. sealed class OperationStatus<T> { object InProgress<T> : OperationStatus<T>() } 16 / 37
17. sealed class OperationStatus<T> { object InProgress<T> : OperationStatus<T>() data class Failure<T>(message: String) : OperationStatus()<T> } 17 / 37
18. sealed class OperationStatus<T> { object InProgress<T> : OperationStatus<T>() data class Failure<T>(message: String) : OperationStatus()<T> data class Success<T>(result: T) : OperationStatus<T>() } 18 / 37
19. Now what? 19 / 37
20. fun showOperationStatus(status: OperationStatus<String>) { when (status) { is InProgress -> showProgress() is Success -> showSuccess(status.result) } } 20 / 37
21. fun showOperationStatus(status: OperationStatus<String>) { when (status) { is InProgress -> showProgress() is Success -> showSuccess(status.result) } } 21 / 37
22. fun showOperationStatus(status: OperationStatus<String>) { when (status) { is InProgress -> showProgress() is Success -> showSuccess(status.result) } } 22 / 37
23. fun showOperationStatus(status: OperationStatus<String>) { when (status) { is InProgress -> showProgress() is Success -> showSuccess(status.result) } } Something is missing... 23 / 37
24. fun showOperationStatus(status: OperationStatus<String>): Unit { return when (status) { // does not compile is InProgress -> showProgress() is Success -> showSuccess(status.result) } } 24 / 37
25. fun showOperationStatus(status: OperationStatus<String>) { return when (status) { is InProgress -> showProgress() is Success -> showSuccess(status.result) is Failure -> showError(status.message) } } 25 / 37
26. car2go 26 / 37
27. sealed class ReservationState { object NoReservation : ReservationState() data class Reserving(vehicleId: String) : ReservationState() data class Cancelling(vehicleId: String) : ReservationState() data class Reserved(vehicleId: String) : ReservationState() sealed class Failure : ReservationState() { object NoInternet : Failure() object NotLoggedIn : Failure() object NotAllowedToDrive : Failure() } } 27 / 37
28. // Either emits value or emits error fun getReservedVehicle(): Observable<Vehicle> // Will crash if error is emitted getReservedVehicle() .subscribe { /* do stuff */ } 28 / 37
29. // Either emits value or emits error fun getReservedVehicle(): Observable<OperationStatus<Vehicle>> // Will not crash, error handled as a value getReservedVehicle() .subscribe { handleReservedVehicleResult(it) } 29 / 37
30. fun handleReservedVehicleResult(result: ReservationStatus) { return when(result) { is NoReservation -> showNoReservation() is Reserving -> showProgressForVehicle(result.vehicleId) // the rest of the types } } 30 / 37
31. To wrap it up Represent one of several possible states. 31 / 37
32. To wrap it up Represent one of several possible states. Forces you to handle all cases. 32 / 37
33. To wrap it up Represent one of several possible states. Forces you to handle all cases. Can be nested. 33 / 37
34. To wrap it up Represent one of several possible states. Forces you to handle all cases. Can be nested. Works great with smart cast. 34 / 37
35. To wrap it up Represent one of several possible states. Forces you to handle all cases. Can be nested. Works great with smart cast. Works great with RxJava 35 / 37
36. To wrap it up Represent one of several possible states. Forces you to handle all cases. Can be nested. Works great with smart cast. Works great with RxJava Not a replacement for every model. 36 / 37
37. Thanks! 37 / 37