Unlocking the Power of Arrow 2.0

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Unlocking the Power of Arrow 2.0 Simon Vergauwen @vergauwen_simon

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ΛRROW Who am I? nomisRev vergauwen_simon vergauwensimon arrow-kt.io

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ΛRROW

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ΛRROW AutoClose

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AutoClose DataSource(config).use { dataSource - > Tracing().use { tracing - > / / use dataSource & tracing } } Why? ΛRROW

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AutoClose DataSource(config).use { dataSource > Tracing().use { tracing > / } } autoCloseScope { val dataSource = install(DataSource(config)) val tracing = install(Tracing()) // use dataSource & tracing } Why? ΛRROW

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AutoClose fun runBlocking( block: suspend CoroutineScope.() -> A ): A How? ΛRROW

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AutoClose fun runBlocking( block: suspend CoroutineScope.() > ): A How? inline fun autoCloseScope( block: AutoCloseScope.() -> A ): A ΛRROW

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AutoCloseScope interface AutoCloseScope { fun install(autoCloseable: A): A } How? ΛRROW

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AutoCloseScope interface AutoCloseScope { fun install(autoCloseable: A): A } ΛRROW Bring your own types!

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AutoCloseScope interface AutoCloseScope { fun install(autoCloseable: A): A } ‣Success: null ‣Cancelled: CancellationException ‣Failed: Throwable Bring your own types! ΛRROW fun autoClose( acquire: () -> A, release: (A, Throwable?) -> Unit ): A

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AutoCloseScope autoCloseScope { val dataSource = install(DataSource(config)) val database = install(Tracing()) // use database & tracing } DSL ΛRROW

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AutoCloseScope Same guarantees as AutoCloseable.use Imperative code, no nesting Bring your own types! Conclusion ΛRROW

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ΛRROW ‣ Raise ‣ Either ‣ NonEmptyList & Set ‣ Ior ‣ Tuple (4-9) ‣ Option AutoClose

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ΛRROW by CashApp AutoClose

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Typed Error Handling ΛRROW Why? class UserExists(message: String): RuntimeException(message) fun insertUser(username: String): User = throw UserExists("User $username already exists.”)

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Typed Error Handling ΛRROW Why? try { insertUser(1) } catch (e: UserExists) { recover(e) }

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Typed Error Handling ΛRROW Why? try { insertUser(1) } catch (e: UserExists) { recover(e) }

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Typed Error Handling interface Raise { fun raise(r: Error): Nothing / / bind, ensure, ensureNotNull, etc. } ΛRROW DSL

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Typed Error Handling ΛRROW How? data class UserExists(val username: String) fun Raise.insertUser(username: String): User = raise(UserExists(username))

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Typed Error Handling ΛRROW Context Parameters data class UserExists(val username: String) context(Raise) fun insertUser(username: String): User = raise(UserExists(username))

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Typed Error Handling inline fun recover( block: Raise.() -> A, recover: (error: Error) -> A, ): A ΛRROW DSL

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Typed Error Handling fun Raise.insertUser(username: String): User = raise(UserExists(username)) ΛRROW recover({ // Raise.() -> User insertUser(“nomisrev") }) { error: UserExists -> null } DSL

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When truly exceptional Fatal exception ( ThreadDeath, VirtualMachineError, …) Unexpected exception, non-business related Type-safety helps protect what you care about Prevent forgetting about business errors Typed Error Handling ΛRROW FAQ : Exception vs Typed Errors?

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Typed Error Handling ΛRROW Example: Exception & Typed context(Raise) suspend fun insertUser(username: String): User = try { queries.insert(username) } catch (e: SQLException) { }

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Typed Error Handling ΛRROW Example: Exception & Typed context(Raise) suspend fun insertUser(username: String): User = try { queries.insert(username) } catch (e: SQLException) { if (e.isUniqueViolation()) raise(UserExists(username)) else throw e }

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Custom models (sealed hierarchies) Use case Layering Context Parameters Typed Error Handling ΛRROW FAQ : How to model errors

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Modelling errors: Sealed hierarchy sealed interface UserError data class UserExists(val username: String): UserError data object UsernameMissing : UserError ΛRROW Use-case

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Modelling errors: Sealed hierarchy sealed interface UserError data class UserExists(val username: String): UserError data object UsernameMissing : UserError ΛRROW Use-case context(Raise) fun HttpRequest.username(): String

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Modelling errors: Sealed hierarchy sealed interface PaymentError data object ExpiredCard : PaymentError data object InsufficientFunds : PaymentError ΛRROW Use-case

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Modelling errors: Sealed hierarchy sealed interface PaymentError data object ExpiredCard : PaymentError data object InsufficientFunds : PaymentError ΛRROW Use-case context(Raise) fun User.receivePayment(): Unit

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Modelling errors: Sealed hierarchy sealed interface UserRegistrationError sealed interface UserError: UserRegistrationError sealed interface PaymentError : UserRegistrationError ΛRROW ( Service) Layering

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Context Parameters suspend fun Raise.route( request: HttpRequest ): HttpResponse { } ΛRROW ( Service) Layering

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Context Parameters suspend fun Raise.route( request: HttpRequest ): HttpResponse { val name = request.username() val user = insertUser(name) user.receivePayment() return HttpResponse.CREATED } ΛRROW ( Service) Layering

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Context Parameters context(Raise, Raise) suspend fun route(request: HttpRequest): HttpResponse { val name = request.username() val user = insertUser(name) user.receivePayment() return HttpResponse.CREATED } ΛRROW Independent errors

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Typed Error Handling ΛRROW Why Raise DSL? A? ≈ Option suspend () -> A ≈ Mono , Single , … suspend FlowCollector .() -> Unit Context Parameters ( KEEP - 367 )

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Typed Error Handling suspend fun refresh(redis: Redis, azure: Azure, custom: Custom) { val message = azure.reactor().awaitSingle() val cache = redis.future().await() delay(100) val res = custom.async().value() TODO() } ΛRROW Combine all the things!

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Typed Error Handling context(Raise) fun everything() { val x = 1.right().bind() val y = ensureNotNull(2) { "Value was null" } ensure(y >= 0) { "y should be >= 0" } val z = quiverOutcome().value() TODO() } ΛRROW Combine all the things!

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context(Raise) fun transaction(): User = transaction { queries.insertUser("nomisrev") } ΛRROW Typed Error Handling Raise = CancellationException

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Typed Error Handling ΛRROW Compile-time check unhappy path Bring your own types! Automatic interoperability with ecosystem Elegantly fits into language Many different error handling strategies Conclusion

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ΛRROW

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ΛRROW Resilience Fx Coroutines Collectors STM Resource

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Schedule var count = 0 var user: User? = null while (isActive) { try { result = insertUser(name) break } catch (e: SQLException) { if (count >= MAX_RETRIES) throw e else delay(BASE_DELAY * 2.0.pow(count ++ )) } } return user ! ! ΛRROW Why?

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Schedule Schedule.exponential(BASE_DELAY) .and(Schedule.recurs(MAX_RETRIES)) .retry { insertUser(name) } ΛRROW How?

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Schedule Schedule.exponential(BASE_DELAY) .and(Schedule.recurs(MAX_RETRIES)) .jittered() .retry { insertUser(name) } ΛRROW Avoid overlapping retries

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Schedule Schedule.exponential(BASE_DELAY) .and(Schedule.recurs(MAX_RETRIES)) .jittered() .doWhile { e: SQLException, _ -> e.isRetryable() } .retry { insertUser(name) } ΛRROW Retry while error is retryable

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Schedule Schedule.exponential(BASE_DELAY) .and(Schedule.recurs(MAX_RETRIES)) .jittered() .doWhile { e: PaymentError, _ -> e.isRetryable() } .retryRaise { raise(ExpiredCard) } ΛRROW Retrying Raise

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Schedule Schedule.recurs(5) .doUntil { response, _ -> response.isCorrect() } .repeat { client.get("my-url") } ΛRROW Repeat 5 times, or until correct result

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Schedule Split Schedule from logic Allows easily building complex Schedules Reuse for repeating, and retrying BONUS : Easy to replace with testing ΛRROW Conclusion

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SagaScope ΛRROW Why? context(Raise) suspend fun route(request: HttpRequest): HttpResponse { val name = request.username() val user = insertUser(name) user.receivePayment() return HttpResponse.CREATED }

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SagaScope ΛRROW Why? context(Raise, SagaScope) suspend fun insertUserOrRollback( username: String ): User

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SagaScope ΛRROW Why? context(Raise, SagaScope) suspend fun insertUserOrRollback( username: String ): User = saga({ insertUser(username) }) { user -> deleteUser(user) }

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SagaScope ΛRROW Why? context(Raise) suspend fun route(request: HttpRequest): HttpResponse { val name = request.username() val user = insertUserOrRollback(name) user.receivePayment() return HttpResponse.OK }

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SagaScope ΛRROW Why? context(Raise) suspend fun route(request: HttpRequest): HttpResponse { val name = request.username() saga { val user = insertUserOrRollback(name) user.receivePayment() }.transact() return HttpResponse.OK }

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SagaScope ΛRROW Why? context(Raise, Transaction) suspend fun route(request: HttpRequest): HttpResponse { val name = request.username() val user = insertUser(name) user.receivePayment() return HttpResponse.CREATED }

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SagaScope ΛRROW Why? fun Routing.premiumUser() = post("/premiumuser/{username}") { recover({ / / Raise.() - > newSuspendedTransaction { // Transaction.() -> route(call) } }) { error -> handleError(error) } }

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SagaScope Saga pattern DSL Avoid distributed transactions Builder for transactional systems ΛRROW Conclusion

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ΛRROW

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ΛRROW Compose KSP Reflect

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Optics data class Product(val id: Long, val price: Double) data class OrderItem(val product: Product, val quantity: Int) Why? ΛRROW

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Optics val item = OrderItem(Product(id = 1, price = 1.5), quantity = 1) item.copy( product = item.product.copy( price = item.product.price * 0.9 ) ) Why? ΛRROW

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Optics val item = OrderItem(Product(id = 1, price = 1.5), quantity = 1) item.copy( product = item.product.copy( price = item.product.price * 0.9 ) ) Why? ΛRROW OrderItem.product.price.modify(item) { it * 1.1 }

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Optics How? ΛRROW data class Inventory(val items: List) inventory.copy( items = inventory.items.map { product -> product.copy(price = product.price * 1.1) } )

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Optics How? ΛRROW Inventory.items.every.price.modify(inventory) { it * 1.1 } data class Inventory(val items: List) inventory.copy( items = inventory.items.map { product > product.copy(price = product.price * 1.1) } )

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Optics How? ΛRROW sealed interface ErrorOrProduct data class Success(val product: Product) : ErrorOrProduct data class Failed(val error: Throwable) : ErrorOrProduct when(errorOrProduct) { is Failed -> errorOrProduct is Success - > Success( errorOrProduct.product .copy(price = errorOrProduct.product.price * 0.9) ) }

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sealed interface ErrorOrProduct data class Success(val product: Product) : ErrorOrProduct data class Failed(val error: Throwable) : ErrorOrProduct when(errorOrProduct) { is Failed > is Success > errorOrProduct.product .copy(price = errorOrProduct.product.price * 1.1) ) } Optics How? ΛRROW ErrorOrProduct.success.product.price.modify(errorOrProduct) { it * 1.1 }

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Optics Multiple fields ΛRROW val item = OrderItem(Product(id = 1, price = 1.5), quantity = 1) item.copy { OrderItem.product.price.transform { it * 1.1 } OrderItem.quantity.set(5) }

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Optics Focus on business logic, and paths Simplify complex immutable transformations KEEP - 237 : Immutability and value classes KT - 44653 by Roman Elisarov “Nicer data transformation with KopyKat and Optics” by Alejandro Serrano ΛRROW Conclusion

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Conclusion What did we learn? ΛRROW Kotlin ❤ DSLs Arrow ❤ Kotlin Small feature specific modules Plug-n-Play: What you want, when you want Much more to learn!

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ΛRROW slack-chats.kotlinlang.org/c/arrow arrow-kt.io github.com/arrow-kt github.com/nomisRev/KotlinConf2024Example Resources Much more to learn!