ITT 2015 - Saul Mora - Object Oriented Function Programming

Functional programming is finally a first class citizen in the Cocoa toolset! But, as you may have heard, Swift is not necessarily a pure functional language. And in embracing the functional paradigm, do you need to throw out your knowledge and experience with Object Oriented programming? Saul Mora shows that it turns out you can have your cake and eat it too!

Transcript

1. Object Oriented Functional Programming Saul Mora smora@coursera.org @casademora
2. Functional Object Oriented Programming Saul Mora smora@coursera.org @casademora
3. Programming Oriented Functional Object Saul Mora smora@coursera.org @casademora
5. Objects
6. C++ Objective C C# Java Ruby Python Javascript PHP
7. Scala! Clojure! Swift
9. Will it blend
10. What a Functional Language is NOT
11. Statically Typed
12. Generic
13. Overloaded Operators
14. Optionals
15. A language where functions are value types
16. F(x) = y
17. f(x: Int) -> Int
19. let numbers = [1, 2, 3, 4, 5] var calculatedNumbers: [Int] = [] for value in numbers { calculatedNumbers.append(value * 2) }
20. map
24. let numbers = [1, 2, 3, 4, 5] let calculatedNumbers = map(numbers) { $0 * 2 }
25. Declarative vs. Imperative
26. What vs. How
27. Deep Dive
28. func old_and_busted_expired(fileURL: NSURL) -> Bool
29. func old_and_busted_expired(fileURL: NSURL) -> Bool { let fileManager = NSFileManager() if let filePath = fileURL.path { if fileManager.fileExistsAtPath(filePath) { var error: NSError? let fileAttributes = fileManager.attributesOfItemAtPath(filePath, error: &error) if let fileAttributes = fileAttributes { if let creationDate = fileAttributes[NSFileModificationDate] as? NSDate { return creationDate.isBefore(NSDate.oneDayAgo()) } } else { NSLog("No file attributes \(filePath)") } } } return false }
30. ! let fileManager = NSFileManager() if let filePath = fileURL.path { if fileManager.fileExistsAtPath(filePath) { var error: NSError? let fileAttributes = fileManager.attributesOfItemAtPath(filePath, error: &error) if let fileAttributes = fileAttributes { if let creationDate = fileAttributes[NSFileModificationDate] as? NSDate { return creationDate .isBefore(NSDate.oneDayAgo()) } } else { NSLog("No file attributes \(filePath)") } }
31. return creationDate.isBefore(NSDate.oneDayAgo())
32. ! let fileManager = NSFileManager() if let filePath = fileURL.path { if fileManager.fileExistsAtPath(filePath) { var error: NSError? let fileAttributes = fileManager.attributesOfItemAtPath(filePath, error: &error) if let fileAttributes = fileAttributes { if let creationDate = fileAttributes[NSFileModificationDate] as? NSDate { return creationDate .isBefore(NSDate.oneDayAgo()) } } else { NSLog("No file attributes \(filePath)") } }
33. unwrapping the file path! check if the file exists! extract and unwrap the file attributes! extract, unwrap and cast the NSModifiedDateAttribute! compute one day ago! return comparison to file last modified date
34. let filePath = fileURL.path
35. let fileExists : (_) -> (_)
36. let fileExists : (String) -> (String?)
37. let fileExists : (String) -> (String?) = { path in fileManager.fileExistsAtPath(path) ? path : nil }
38. let retrieveFileAttributes : (_) -> (_)
39. let retrieveFileAttributes : (String) -> ([NSObject: AnyObject]?)
40. let retrieveFileAttributes : (String) -> ([NSObject: AnyObject]?) = { path in var error : NSError? let attributes = fileManager.attributesOfItemAtPath(path, error: &error) ! if attributes == nil { NSLog("Unable to check \(filePath): \(error)") } return attributes }
41. let extractCreationDate : (_) -> (_)
42. let extractCreationDate : ([NSObject:AnyObject]) -> (NSDate?)
43. let extractCreationDate : [NSObject:AnyObject] -> NSDate? = { $0[NSFileModificationDate] as? NSDate }
44. filePath: String? fileExists: String -> String? extractFileAttributes: String -> [NSObject:AnyObject]? extractCreationDate: [NSObject:AnyObject] -> NSDate?
45. let filePath: String? let fileExists: String -> String? let extractFileAttributes: String -> [NSObject:AnyObject]? let extractCreationDate: [NSObject:AnyObject] -> NSDate?
46. bind
47. bind(A?, f(A,B?)) -> B?
48. func bind<A, B>(a: A?, f: A -> B?) -> B? { if let x = a { return f(x) } else { return .None } }
49. bind(filePath, fileExists)
50. bind(bind(filePath, fileExists), retrieveFileAttributes)
51. bind(bind(bind(filePath, fileExists), retrieveFileAttributes), extractCreationDate)
52. let creationDate: NSDate? = bind(bind(bind(filePath, fileExists), retrieveFileAttributes), extractCreationDate)
53. >>= operator
54. func >>=<A, B>(a: A?, f: A -> B?) -> B? { return bind(a, f) }
55. bind(filePath, fileExists)
56. filePath >>= fileExists
57. if let creationDate = filePath >>= fileExists >>= retrieveFileAttributes >>= extractCreationDate { return creationDate.isBefore(NSDate.oneDayAgo()) }
58. let checkExpired: NSDate -> Bool? = { $0.isBefore(NSDate.oneDayAgo()) }
59. return filePath >>= fileExists >>= retrieveFileAttributes >>= extractCreationDate >>= checkExpired ?? false
60. func expired(fileURL: NSURL) -> Bool { let fileManager = NSFileManager() var error : NSError? let filePath = fileURL.path let fileExists : (String) -> (String?) = { path in fileManager.fileExistsAtPath(path) ? path : nil } let retrieveFileAttributes : (String) -> ([NSObject: AnyObject]?) = { path in var error : NSError? return fileManager.attributesOfItemAtPath(path, error: &error) } let extractCreationDate : ([NSObject:AnyObject]) -> NSDate? = { $0[NSFileModificationDate] as? NSDate } let checkExpired: NSDate -> Bool? = { $0.isBefore(NSDate.oneDayAgo()) } return filePath >>= fileExists >>= retrieveFileAttributes >>= extractCreationDate >>= checkExpired ?? false }
61. Readability
62. bind! flatMap (fmap)! apply >>= (>>-)! <^> (<$>)! <*>
63. func <^><A, B>(f: A -> B, a: A?) -> B? { return fmap(f, a) } ! func fmap<A, B>(f: A -> B, a: A?) -> B? { if let x = a { return f(x) } else { return .None } }
64. func <*><A, B>(f: (A -> B)?, a: A?) -> B? { return apply(f, a) } ! func apply<A, B>(f: (A -> B)?, a: A?) -> B? { if let x = a, let fx = f { return fx(x) } return .None }
65. Argo http://github.com/thoughtbot/Argo
66. What about objects?
67. Caching
68. retrieve
69. protocol DataSource { func fetchItem() -> Int? } ! func retrieve<S: DataSource, T>(from: S, or: S) -> T? { return from.fetchItem() ?? or.fetchItem() }
70. protocol DataSource { func fetchItem() -> Int? } ! func retrieveItem<S: DataSource, T>(from: S, or: S) -> T? { return from.fetchItem() ?? or.fetchItem() }
71. return <DataSource>! .functionCall()! -> Int?
72. ! func retrieve<S: DataSource, T> (from: S, or: S, using: S -> T?) -> T? { return using(from) ?? using(or) }
73. let localDataSource: DataSource let remoteDataSource: DataSource return retrieve(from: localDataSource, or: remoteDataSource) { $0.fetchItem() }
74. Data Client RemoteDataSource LocalDataSource
75. Data Client RemoteDataSource LocalDataSource
76. Data Client RemoteDataSource LocalDataSource DataSourceCache
77. Data Client RemoteDataSource LocalDataSource DataSourceCache Cache Strategy
78. protocol DataSourceCacheStrategy { func retrieve<T>(from: [DataSource], using: DataSource -> T?) -> T? } ! struct DataSourceCache { let strategy: DataSourceCacheStrategy let localDataSource: DataSource let remoteDataSource: DataSource func fetch<T>(applyFunction: DataSource -> T?) -> T? { let sources = [localDataSource, remoteDataSource] return strategy.retrieve(sources, using: applyFunction) } }
79. struct BasicDataSourceCacheStrategy: DataSourceCacheStrategy { func retrieve<T>(from: [DataSource], using: DataSource -> T?) -> T? { for dataSource in from { if let result = using(dataSource) { return result } } return nil } }
80. struct MoreFancyDataSourceCacheStrategy: DataSourceCacheStrategy { ! func retrieve<T>(from: [DataSource], using: DataSource -> T?) -> T? { let cacheValidation: T? -> Bool = { $0 != nil } for dataSource in from { let result = using(dataSource) if cacheValidation(result) { return result } } return nil } }
81. https://gist.github.com/ casademora/ 3b784e57bd09c0bc9147
82. Encapsulation
83. Abstraction
84. SOLID
85. Object Oriented in the Large, Functional in the Small
86. - Alan Kay, The Early History of Smalltalk I was less interested in programs as algebraic patterns than I was in a clear scheme that could handle a variety of styles of programming.
87. Programming
88. –Alan Kay Programming is at heart a practical art in which real things are built, and a real implementation thus has to exist.
89. Object Oriented Functional Programming Saul Mora smora@coursera.org @casademora