This document discusses functional programming in Swift and compares it to object-oriented programming. It provides examples of common functional programming techniques like map, filter, and reduce implemented in both FP and OO styles in Swift. It also discusses using functional programming concepts like immutable data and pure functions for handling asynchronous requests by transforming Observables.

1. Programação Funcional na
Prática com Swift
Rodrigo Amorim Ruiz
Vikki (vikki.ai)

2. Porque Swift
• Passagem por valor
• Tipagem estática + inferência
• Optional
• Lambda e outras construções de FP
• Enum

3. VS
Programação Orientada a Objetos
Programação Funcional
Comparação

4. Considerações
• Swift vs Cocoa
• Questão de estilo
• OO / Procedural / Imperativo
• Técnicas de FP em OO
• Performance
• Leitura vs Escrita
• Melhor ferramenta para cada problema

5. Programação Funcional Programação Orientada a ObjetosVS

6. Programação Funcional Programação Orientada a ObjetosVS

8. Motivos

10. Class vs Struct
// OO
func customPrint(person: Person) {
DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(10), execute: {
print("After 10 seconds: (person.name)")
})
}
class Person {
var name: String
init(name: String) {
self.name = name
}
}
let p = Person(name: "Rodrigo")
customPrint(person: p)
p.name = "Thomas"
print(p.name)

11. Class vs Struct
// FP
func customPrint(person: Person) {
DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(10), execute: {
print("After 10 seconds: (person.name)")
})
}
struct Person {
var name: String
}
let p = Person(name: "Rodrigo")
customPrint(person: p)
p.name = "Thomas"
print(p.name)

12. Map
// OO
var values = [Double]()
for step in steps {
values.append(sin(Double(step) / 10))
}
print(values)
// FP
let values = steps.map({ sin(Double($0) / 10) })
print(values)
let steps = (1...100)

13. Filter
// OO
var partyFriends = [String]()
for friend in friends {
if friend.age >= 18 && friend.age <= 40 {
partyFriends.append(friend.name)
}
}
print(partyFriends)
// FP
let partyFriends = friends
.filter({ $0.age >= 18 && $0.age <= 40 })
.map({ $0.name })
print(partyFriends)
let friends = [
(name: "Pedro", age: 12),
(name: "Maria", age: 18),
(name: "João", age: 21),
(name: "Regina", age: 55)
]

14. Reduce
// OO
var totalMoney = 0
for money in moneyPile {
totalMoney += money
}
var text = ""
for character in characters {
text += character
}
print(totalMoney)
print(text)
// FP
let totalMoney = moneyPile.reduce(0, +)
let text = characters.reduce("", +)
print(totalMoney)
print(text)
let moneyPile = [10, 20, 15, 30]
let characters = ["a", "b", "c", "d"]

15. Count Words
// Procedural
let content = readFile()
let words = content.split(separator: " ")
var tally = [String: Int]()
for word in words {
let lowerCaseWord = word.lowercased()
tally[lowerCaseWord] = (tally[lowerCaseWord] ?? 0) + 1
}
var tallyAsArray = [(word: String, count: Int)]()
for (key, value) in tally {
tallyAsArray.append((word: key, count: value))
}
tallyAsArray.sort(by: { $0.count > $1.count })
var top10 = [(word: String, count: Int)]()
for i in (0..<10) {
top10.append(tallyAsArray[i])
}
for value in top10 {
print("(value.word) - (value.count)")
}

16. Count Words
// OO
class WordCounter {
func printTop10() {
readFileToContent()
splitContentIntoWords()
createTally()
sortTally()
getTop10Words()
printTop10()
}
private var content = ""
private var words = [String.SubSequence]()
private var tally = [String: Int]()
private var tallyAsArray = [(word: String, count: Int)]()
private var top10 = [(word: String, count: Int)]()
private func readFileToContent() { … }
private func splitContentIntoWords() { … }
private func createTally() { … }
private func sortTally() { … }
private func getTop10Words() { … }
private func printTop10Words() { … }
}
let w = WordCounter()
w.printTop10()

17. Count Words
// FP
let output = readFile()
.split(separator: " ")
.map({ $0.lowercased() })
.reduce([String: Int](), { (tally, lowerCaseWord) in
return tally.merging(
[lowerCaseWord: (tally[lowerCaseWord] ?? 0) + 1],
uniquingKeysWith: { $1 }
)
})
.sorted(by: { $0.value > $1.value })
.prefix(10)
.map({ "($0.key) - ($0.value)" })
.joined(separator: "n")
print(output)

18. Requests (OO)
let party = CreateParty(delegate: CreatePartyDelegate())
party.create()
class CreateParty: SendAPIRequestDelegate {
init(delegate: CreatePartyDelegate) {
self.delegate = delegate
self.friendsRequest = SendAPIRequest(url: "https://api.com/friends", delegate: self)
self.placeRequest = SendAPIRequest(url: "https://api.com/place", delegate: self)
}
func create() {
self.friendsRequest.request()
self.placeRequest.request()
}
...
}

19. Requests (OO)
class CreateParty: SendAPIRequestDelegate {
...
// MARK: - SendAPIRequestDelegate
func success(request: SendAPIRequest, json: JSON) {
if request === self.friendsRequest {
self.friends = json.array!.map(toString)
friendsReady = true
tryToCreatePartyData()
}
if request === self.placeRequest {
self.place = json.string!
placeReady = true
tryToCreatePartyData()
}
}
func failure(request: SendAPIRequest, error: APIRequestError) {
if request === self.friendsRequest {
friendsReady = true
tryToCreatePartyData()
}
if request === self.placeRequest {
placeReady = true
tryToCreatePartyData()
}
}
...
}

20. Requests (OO)
class CreateParty: SendAPIRequestDelegate {
...
// MARK: - Private
private var friendsRequest: SendAPIRequest!
private var placeRequest: SendAPIRequest!
private var friendsReady = false
private var placeReady = false
private var friends: [String]?
private var place: String?
private let delegate: CreatePartyDelegate
private var party: Party?
private func tryToCreatePartyData() {
if !self.friendsReady || !self.placeReady {
return
}
if let friends = self.friends, let place = self.place {
self.party = Party(friends: friends, place: place)
} else {
self.party = nil
}
callDelegateWithPartyData()
}
...
}

21. Requests (OO)
class CreatePartyDelegate {
func printNoParty() {
print("There will be no party.")
}
func printParty(party: Party) {
print("Go party!!!")
print("Place: (party.place)")
print("Friends:")
for friend in party.friends {
print(friend)
}
}
}
class CreateParty: SendAPIRequestDelegate {
...
// MARK: - Private
...
private func callDelegateWithPartyData() {
guard let party = self.party else {
delegate.printNoParty()
return
}
delegate.printParty(party: party)
}
}

22. Requests (FP1)
let friendsObservable = sendAPIRequest(url: "https://api.com/friends")
.map(getSuccess >>> map(toArray >>> map(toString)))
let placeObservable = sendAPIRequest(url: "https://api.com/place")
.map(getSuccess >>> map(toString))
let partyObservable = Observable
.zip(friendsObservable, placeObservable)
.map(mergeOptionals >>> map(applyTuple(Party.init)))
let outputObservable = partyObservable.map(
map({
"Go party!!!n"
+ "Place: ($0.place)n"
+ "Friends:n"
+ $0.friends.joined(separator: "n")
})
>>> defaultTo("There will be no party.")
)
_ = outputObservable.subscribe(onNext: { print($0) })

23. Requests (FP2)
(
"https://api.com/friends",
"https://api.com/place"
)
>>> both(sendAPIRequest >>> map(getSuccess))
>>> first(map(map(toArray >>> map(toString))))
>>> second(map(map(toString)))
>>> applyTuple(Observable.zip)
>>> map(mergeOptionals >>> map(applyTuple(Party.init)))
>>> map(
map({
"Go party!!!n"
+ "Place: ($0.place)n"
+ "Friends:n"
+ $0.friends.joined(separator: "n")
})
>>> defaultTo("There will be no party.")
)
>>> subscribe(onNext: { print($0) })

24. Requests (FP2’)
let mapFriends: (Observable<JSON?>) -> Observable<[String]?> = map(map(toArray >>> map(toString)))
let mapPlace: (Observable<JSON?>) -> Observable<String?> = map(map(toString))
let requests = both(sendAPIRequest >>> map(getSuccess))
>>> first(mapFriends)
>>> second(mapPlace)
let createParty: ((Observable<[String]?>, Observable<String?>)) -> Observable<Party?> =
applyTuple(Observable.zip)
>>> map(mergeOptionals >>> map(applyTuple(Party.init)))
let toOutputString: (Observable<Party?>) -> Observable<String> = map(
map({
"Go party!!!n"
+ "Place: ($0.place)n"
+ "Friends:n"
+ $0.friends.joined(separator: "n")
})
>>> defaultTo("There will be no party.")
)
let requestStringsToOutput = requests
>>> createParty
>>> toOutputString
_ = requestStringsToOutput((
"https://api.com/friends",
"https://api.com/place"
)).subscribe(onNext: { print($0) })

25. AI

26. Conceitos Utilizados
• Dados x Comportamento
• Imperativo vs Declarativo
• Funções puras
• Imutabilidade
• Funções de alta ordem
• Functors, Applicatives e Monads
• Maybe (Optional)
• Array
• Result
• Promise / Observable

27. Haskell vs. Ada vs. C++ vs. Awk vs. ...
An Experiment in Software Prototyping
Productivity∗
Paul Hudak Mark P. Jones
Yale University
Department of Computer Science
New Haven, CT 06518 {hudak-paul,jones-mark}@cs.yale.edu
July 4, 1994

28. https://www.linkedin.com/in/rodrigoaruiz/