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!

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