JSON + Swift: Functionally Beautiful

An exploration into the functional way of parsing JSON in Swift. Link to download the playground: https://github.com/abijlani/json-swift

Transcript

1. Amit Bijlani @paradoxed Amit Bijlani, @paradoxed - 2015
2. JSON + Swift Functionally Beautiful Amit Bijlani, @paradoxed - 2015
3. Treehouse teamtreehouse.com Amit Bijlani, @paradoxed - 2015
4. JSON Parsing Amit Bijlani, @paradoxed - 2015
5. JSON Parsing var jsonError: NSError? let jsonObject: AnyObject! = NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers, error: &jsonError) Amit Bijlani, @paradoxed - 2015
6. Twitter Timeline [ { "user": { "name": "OAuthDancer", "profile_sidebar_fill_color": "DDEEF6", "profile_background_tile": true, "profile_sidebar_border_color": "C0DEED", "created_at": "WedMar0319: 37: 35+00002010", "location": "SanFrancisco, CA", "follow_request_sent": false, "is_translator": false, "profile_link_color": "0084B4", "entities": { "url": { "urls": [ { "expanded_url": null, "url": "http: //bit.ly/oauth-dancer", "display_url": null } ] }, }, }, } ] Amit Bijlani, @paradoxed - 2015
7. Parsing Data func parseData(data: NSData?) -> String? { var jsonError: NSError? let jsonObject: AnyObject! = NSJSONSerialization.JSONObjectWithData(...) if let err = jsonError { return nil } if let statuses = jsonObject as? Array<AnyObject> { if let aStatus = statuses[0] as? Dictionary<String, AnyObject> { if let user = aStatus["user"] as? Dictionary<String, AnyObject> { if let username = user["name"] { //Finally We Get The Username return username } } } } // if all else fails return nil return nil } Amit Bijlani, @paradoxed - 2015
8. if-let Pyramid of doom! if let statuses = jsonObject as? Array<AnyObject> { if let aStatus = statuses[0] as? Dictionary<String, AnyObject> { if let user = aStatus["user"] as? Dictionary<String, AnyObject> { if let username = user["name"] { //Finally We Get The Username return username } } } } Amit Bijlani, @paradoxed - 2015
9. if-let Swift 1.2 if let statuses = jsonObject as? Array<AnyObject>, aStatus = statuses[0] as? Dictionary<String, AnyObject>, user = aStatus["user"] as? Dictionary<String, AnyObject>, username = user["name"] as? String { //Finally We Get The Username return username } Amit Bijlani, @paradoxed - 2015
10. Drawbacks • Large if-let statement leads to fragile code and legibility issues • A lot of code is repeated: • Checking for Optionals • Type conversions Amit Bijlani, @paradoxed - 2015
11. Taming the Beast Amit Bijlani, @paradoxed - 2015
12. Key Data Types AnyObject Dictionary<String,AnyObject> Array<AnyObject> Amit Bijlani, @paradoxed - 2015
13. Using Typealias typealias JSON = AnyObject typealias JSONDictionary = Dictionary<String, JSON> typealias JSONArray = Array<JSON> Amit Bijlani, @paradoxed - 2015
14. Extracting Information Somewhat Cleaner if let statuses = jsonObject as? JSONArray, aStatus = statuses[0] as? JSONDictionary, user = aStatus["user"] as? JSONDictionary, username = user["name"] as? String { return username } Amit Bijlani, @paradoxed - 2015
15. Error Handling func parseData(data: NSData?) -> String? { var jsonError: NSError? let jsonObject: AnyObject! = NSJSONSerialization.JSONObjectWithData(...) if let err = jsonError { return nil } if let statuses = jsonObject as? JSONArray, aStatus = statuses[0] as? JSONDictionary, user = aStatus["user"] as? JSONDictionary, username = user["name"] as? String { return username } // if all else fails return nil return nil } Amit Bijlani, @paradoxed - 2015
16. Something or Nothing Amit Bijlani, @paradoxed - 2015
17. Optional enum Optional<T> { case None case Some(T) } Amit Bijlani, @paradoxed - 2015
18. Error Handling Either - Failed to parse the JSON? Or - Successfully parsed the JSON Amit Bijlani, @paradoxed - 2015
19. Either Type enum Either<A, B> { case Left(A) case Right(B) } • Left represents failure • Right represents the correct value Amit Bijlani, @paradoxed - 2015
20. Result Enum enum Result<A> { case Error(NSError) case Value(A) // causes runtime errors } Amit Bijlani, @paradoxed - 2015
21. Container Class final class Box<A> { let value: A init(_ value: A) { self.value = value } } enum Result<A> { case Error(NSError) case Value(Box<A>) } Amit Bijlani, @paradoxed - 2015
22. Result Enum func parseData(data: NSData?, callback: (Result<String>) -> ()) { var jsonError: NSError? let jsonObject: AnyObject! = NSJSONSerialization.JSONObjectWithData(...) if let err = jsonError { callback(.Error(err)) return } if let statuses = jsonObject as? JSONArray, aStatus = statuses[0] as? JSONDictionary, user = aStatus["user"] as? JSONDictionary, username = user["name"] as? String { callback(.Value(Box(userName))) return } callback(.Error(NSError())) // pass a specific error } Amit Bijlani, @paradoxed - 2015
23. Calling parseData // func parseData(data: NSData?, callback: (Result<String>) -> ()) parseData(data, {(result: Result<String>) -> () in switch result { case let .Error(err): println("Error") case let .Value(userName): println(userName.value) } }) Amit Bijlani, @paradoxed - 2015
24. Calling parseData // func parseData(data: NSData?, callback: (Result<String>) -> ()) // Trailing closure parseData(data) {result in switch result { case let .Error(err): println("Something went wrong!") case let .Value(userName): println(userName.value.name) } } Amit Bijlani, @paradoxed - 2015
25. Clearing up Casting if let statuses = jsonObject as? JSONArray, aStatus = statuses[0] as? JSONDictionary, user = aStatus["user"] as? JSONDictionary, username = user["name"] as? String { callback(.Value(Box(username))) return } Amit Bijlani, @paradoxed - 2015
26. Creating Cast Functions func JSONToString(object: JSON?) -> String? { return object as? String } func JSONToInt(object: JSON?) -> Int? { return object as? Int } func JSONToDictionary(object: JSON?) -> JSONDictionary? { return object as? JSONDictionary } func JSONToArray(object: JSON?) -> JSONArray? { return object as? JSONArray } Amit Bijlani, @paradoxed - 2015
27. Using Cast Functions if let statuses = JSONToArray(jsonObject), aStatus = JSONToDictionary(statuses[0]), user = JSONToDictionary(aStatus["user"]), username = JSONToString(user["name"]) { callback(.Value(Box(username))) return } Amit Bijlani, @paradoxed - 2015
28. Diving into Functional Programming Warning custom operators ahead! Amit Bijlani, @paradoxed - 2015
29. Monads Bind Operator Amit Bijlani, @paradoxed - 2015
30. For Example func half(x: Int) -> Int? { // if x is even return x/2 if x % 2 == 0 { return x / 2 } return .None } Amit Bijlani, @paradoxed - 2015
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33. Monads in Swift Binds an Optional to a Function that takes a non-optional and returns an Optional A? >>> A -> B? -> B? Amit Bijlani, @paradoxed - 2015
34. Monads in Swift func monad<A, B>(a: A?, f: A -> B?) -> B? Amit Bijlani, @paradoxed - 2015
35. Monads Bind Operator infix operator >>> { associativity left precedence 150 } func >>><A, B>(a: A?, f: A -> B?) -> B? { if let x = a { return f(x) } else { return .None } } Amit Bijlani, @paradoxed - 2015
36. Modifying Cast Functions To accept non-optional parameters func JSONToString(object: JSON) -> String? { return object as? String } func JSONToInt(object: JSON) -> Int? { return object as? Int } func JSONToDictionary(object: JSON) -> JSONDictionary? { return object as? JSONDictionary } func JSONToArray(object: JSON) -> JSONArray? { return object as? JSONArray } Amit Bijlani, @paradoxed - 2015
37. Using the Bind Operator if let statuses = jsonObject >>> JSONToArray, aStatus = statuses[0] >>> JSONToDictionary, user = aStatus["user"] >>> JSONToDictionary, username = user["name"] >>> JSONToString { callback(.Value(Box(username))) return } Amit Bijlani, @paradoxed - 2015
38. Let's make it a bit more interesting Amit Bijlani, @paradoxed - 2015
39. User Model struct User { let name: String let profileDescription: String let followersCount: Int ... } Amit Bijlani, @paradoxed - 2015
40. Creating a User Object if let statuses = jsonObject >>> JSONToArray, aStatus = statuses[0] >>> JSONToDictionary, user = aStatus["user"] >>> JSONToDictionary { if let username = user["name"] >>> JSONToString, let profileDescription = user["description"] >>> JSONToString, let followersCount = user["followers_count"] >>> JSONToInt { let u = User( username: username, profileDescription: profileDescription, followersCount: followersCount ) { callback(.Value(Box(u))) return } } } Amit Bijlani, @paradoxed - 2015
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42. More Functional Goodness • Functors fmap <^> • Applicatives functors apply <*> Amit Bijlani, @paradoxed - 2015
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45. How does one add to an Optional? Amit Bijlani, @paradoxed - 2015
46. fmap applying functions to values wrapped in an Optional Amit Bijlani, @paradoxed - 2015
47. fmap Amit Bijlani, @paradoxed - 2015
48. Implementing fmap infix operator <^> { associativity left } // fmap (usually <$>) //func >>><A, B>(a: A?, f: A -> B?) -> B? // bind operator func <^><A, B>(f: A -> B, a: A?) -> B? { if let x = a { return f(x) } else { return .None } } Amit Bijlani, @paradoxed - 2015
49. apply applying wrapped functions to values wrapped in some context Amit Bijlani, @paradoxed - 2015
50. Implementing apply infix operator <*> { associativity left } // apply func <*><A, B>(f: (A -> B)?, a: A?) -> B? { if let x = a { if let fx = f { return fx(x) } } return .None } Amit Bijlani, @paradoxed - 2015
51. Currying "If we give a function fewer parameters than it takes, it will return a function that takes the remaining parameters" struct User { let name: String let profileDescription: String let followersCount: Int static func create(name: String)(profileDescription: String)(followersCount: Int) -> User { return User(name: name, profileDescription: profileDescription, followersCount: followersCount) } } Amit Bijlani, @paradoxed - 2015
52. Behold if let statuses = jsonObject >>> JSONToArray, aStatus = statuses[0] >>> JSONToDictionary, userDictionary = aStatus["user"] >>> JSONToDictionary { let user = User.create <^> userDictionary["name"] >>> JSONToString <*> userDictionary["description"] >>> JSONToString <*> userDictionary["followers_count"] >>> JSONToInt { if let u = user { callback(.Value(Box(u))) return } } } Amit Bijlani, @paradoxed - 2015
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54. Avoiding Multiple Returns func parseData(data: NSData?, callback: (Result<User>) -> ()) { var jsonError: NSError? let jsonObject: AnyObject! = NSJSONSerialization.JSONObjectWithData(...) if let err = jsonError { callback(.Error(err)) return } if let statuses = jsonObject >>> JSONToArray, aStatus = statuses[0] >>> JSONToDictionary, userDictionary = aStatus["user"] >>> JSONToDictionary { let user = User.create <^> userDictionary["name"] >>> JSONToString <*> userDictionary["description"] >>> JSONToString <*> userDictionary["followers_count"] >>> JSONToInt if let u = user { callback(.Value(Box(u))) return } } callback(.Error(NSError())) } Amit Bijlani, @paradoxed - 2015
55. Breaking up the function • Parse the response • Parse the data into JSON • Parse the JSON into our User object Amit Bijlani, @paradoxed - 2015
56. Don't reinvent the Wheel • Argo • Swifty JSON Amit Bijlani, @paradoxed - 2015
57. Argo Example struct User { let name: String let email: String? let role: Role } extension User: JSONDecodable { static func create(name: String)(email: String?)(role: Role) -> User { return User(name: name, email: email, role: role) } static func decode(j: JSONValue) -> User? { return User.create <*> j <| "name" <*> j <|? "email" // Use ? for parsing optional values <*> j <| "role" // Custom types that also conform to JSONDecodable just work } } Amit Bijlani, @paradoxed - 2015
58. Argo Example let json: AnyObject? = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions(0), error: .None) if let j: AnyObject = json { let value = JSONValue.parse(j) let user = User.decode(value) } Amit Bijlani, @paradoxed - 2015
59. SwiftyJSON let json = JSON(data: dataFromNetworking) if let userName = json[0]["user"]["name"].string{ //Now you got your value print(userName) } Amit Bijlani, @paradoxed - 2015
60. Thank You! • http://robots.thoughtbot.com/efficient-json-in-swift-with- functional-concepts-and-generics • https://github.com/thoughtbot/Argo • https://github.com/SwiftyJSON/SwiftyJSON • http://www.objc.io/books/ Amit Bijlani, @paradoxed - 2015