Object Oriented Functional Programming — Saul Mora

Functional programming is finally a first class citizen in the Cocoa toolset! But, Swift is not necessarily a pure functional language. And in embracing the functional paradigm, do we need to throw out our knowledge and experience with Object Oriented programming? It turns out we can have our cake and eat it too!

This talk was presented at AltConf in June 2015.

Transcript

1. Object Oriented Functional Programming Saul Mora saul@casademora.com @casademora
2. Functional Object Oriented Programming Saul Mora saul@casademora.com @casademora
3. Programming Oriented Functional Object Saul Mora saul@casademora.com @casademora
4. Objects
5. C++ Objective C C# Java Ruby Python Javascript PHP
6. Scala Clojure Swift
8. Will it blend
9. What a Functional Language is NOT
10. Statically Typed
11. Generics
12. Overloaded Operators
13. Optionals
14. A language where functions are value types
15. Objective C is a Functional Language
16. F(x) = y
17. f(x: Int) -> Int
19. map
23. let numbers = [1, 2, 3, 4, 5] var calculatedNumbers: [Int] = [] for value in numbers { calculatedNumbers.append(value * 2) }
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. 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
32. let filePath = fileURL.path
33. let fileExists : (_) -> (_)
34. let fileExists : (String) -> (String?)
35. let fileExists : (String) -> (String?) = { path in fileManager.fileExistsAtPath(path) ? path : nil }
36. let retrieveFileAttributes : (_) -> (_)
37. let retrieveFileAttributes : (String) -> ([NSObject: AnyObject]?)
38. 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 }
39. let extractCreationDate : (_) -> (_)
40. let extractCreationDate : ([NSObject:AnyObject]) -> (NSDate?)
41. let extractCreationDate : [NSObject:AnyObject] -> NSDate? = { $0[NSFileModificationDate] as? NSDate }
42. let filePath: String? let fileExists: String -> String? let extractFileAttributes: String -> [NSObject:AnyObject]? let extractCreationDate: [NSObject:AnyObject] -> NSDate?
43. Composition
44. bind
45. bind(A?, f(A) -> B?) -> B?
46. func bind<A, B>(a: A?, f: A -> B?) -> B? { if let x = a { return f(x) } else { return .None } }
47. bind(filePath, fileExists)
48. bind(bind(filePath, fileExists), retrieveFileAttributes)
49. bind(bind(bind(filePath, fileExists), retrieveFileAttributes), extractCreationDate)
50. let creationDate: NSDate? = bind(bind(bind(filePath, fileExists), retrieveFileAttributes), extractCreationDate)
51. >>= operator
52. func >>=<A, B>(a: A?, f: A -> B?) -> B? { return bind(a, f) }
53. bind(filePath, fileExists)
54. filePath >>= fileExists
55. if let creationDate = filePath >>= fileExists >>= retrieveFileAttributes >>= extractCreationDate { return creationDate.isBefore(NSDate.oneDayAgo()) }
56. let checkExpired: NSDate -> Bool? = { $0.isBefore(NSDate.oneDayAgo()) }
57. return filePath >>= fileExists >>= retrieveFileAttributes >>= extractCreationDate >>= checkExpired ?? false
58. 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? = { $0.isBefore(NSDate.oneDayAgo()) } return filePath >>= fileExists >>= retrieveFileAttributes >>= extractCreationDate >>= checkExpired ?? false }
59. Railway Oriented Programming fsharpforfunandprofit.com/posts/recipe-part2/
60. Readability
61. bind flatMap (fmap) apply >>= >>- <^> <$> <*>
62. 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 } }
63. 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 }
64. Argo http://github.com/thoughtbot/Argo
65. What about objects?
66. Objects > Functions
67. Objects ≈ Functions
68. Caching
69. retrieve
70. Data Client RemoteDataSource LocalDataSource
71. Data Client RemoteDataSource LocalDataSource
72. Data Client RemoteDataSource LocalDataSource DataSourceCache
73. Data Client RemoteDataSource LocalDataSource DataSourceCache Cache Strategy
74. Strategy
75. protocol DataSource { func fetchItem() -> Int? } func retrieve<S: DataSource, T>(from: S, or: S) -> T? { return from.fetchItem() ?? or.fetchItem() }
76. protocol DataSource { func fetchItem() -> Int? } func retrieveItem<S: DataSource, T>(from: S, or: S) -> T? { return from.fetchItem() ?? or.fetchItem() }
77. from.fetchItem()
78. from .fetchItem() Object Instance Selector
79. func retrieve<S: DataSource, T> (from: S, or: S, using: S -> T?) -> T? { return using(from) ?? using(or) }
80. let localDataSource: DataSource let remoteDataSource: DataSource return retrieve(from: localDataSource, or: remoteDataSource) { $0.fetchItem() }
81. 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) } }
82. 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 } }
83. 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 } }
84. Encapsulation
85. Abstraction
86. SOLID
87. Object Oriented in the Large, Functional in the Small
88. Stuff that changes vs. Stuff that doesn’t
89. Functional Friendly Problem Domains
90. - 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.
91. Object Oriented Programming Functional Programming
92. Programming Object Oriented Programming Functional Programming
93. –Alan Kay Programming is at heart a practical art in which real things are built, and a real implementation thus has to exist.
94. Object Oriented Functional Programming Saul Mora saul@casademora.com @casademora