Let’s Functional Programing in Your Swift Code

Let’s Functional Programing in Your Swift Code by UJ Cheng @ iPlayground 2025

Transcript

1. Let’s Functional Programing in Your Swift Code Follow「iamhands0me」on U. J. Cheng, Advanced Software Engineer @
2. Scenario Given an array of scores, apply square root scaling (√𝒔×𝟏𝟎) and sum the results that are ≥ 60 func sum(scores: [Int]) -> Double { var total: Double = 0 for score in scores { let scaled = sqrt(Double(score)) * 10 if scaled >= 60 { total += scaled } } return total } func sum(scores: [Int]) -> Double { scores .map { sqrt(Double($0)) * 10 } .filter { $0 >= 60 } .reduce(0, +) }
3. Functional Programing Higher Order Functions Closure Expression Function Chaining Single-Expression (with return omitted) 1-liner 一句話 func sum(scores: [Int]) -> Double { scores .map { sqrt(Double($0)) * 10 } .filter { $0 >= 60 } .reduce(0, +) }
4. https://developer.apple.com/documentation/swift/array#Transforming-an-Array Array Transforming
5. flatMap(_:) let numbers = [1, 2, 3, 4] let mapped: [[Int]] = numbers.map { Array(repeating: $0, count: $0) } // [[1], [2, 2], [3, 3, 3], [4, 4, 4, 4]] let flatMapped: [Int] = numbers.flatMap { Array(repeating: $0, count: $0) } // [1, 2, 2, 3, 3, 3, 4, 4, 4, 4]
6. let possibleNumbers = ["1", "2", "three", "///4///", "5"] let mapped: [Int?] = possibleNumbers.map { Int($0) } // [1, 2, nil, nil, 5] let compactMapped: [Int] = possibleNumbers.compactMap { Int($0) } // [1, 2, 5] compactMap(_:)
7. https://developer.apple.com/documentation/swift/array#Reordering-an-Arrays-Elements Array Reordering
8. sorted(by:) let students: Set = ["Kofi", "Abena", "Peter", "Kweku", "Akosua"] let descendingStudents = students.sorted(by: >) print(descendingStudents) // Prints ["Peter", "Kweku", "Kofi", "Akosua", "Abena"]
9. reversed() let word = "Backwards" for char in word.reversed() { print(char, terminator: "") } // Prints "sdrawkcaB" let reversedWord = word.reversed() print(reversedWord) // Prints ReversedCollection<String>(_base: "Backwards")
10. reversed() let word = "Backwards" for char in word.reversed() { print(char, terminator: "") } // Prints "sdrawkcaB" let reversedWord = word.reversed() print(reversedWord) // Prints ReversedCollection<String>(_base: "Backwards") "Backwards" String ReversedCollection<String>
11. https://developer.apple.com/documentation/swift/array#Finding-Elements Array Finding
12. contains(where:) let scores = [75, 51, 84, 93, 50] if !scores.contains(where: { $0 < 60 }) { print("All Pass!") }
13. allSatisfy(_:) let scores = [75, 51, 84, 93, 50] if scores.allSatisfy({ $0 >= 60 }) { print("All Pass!") }
14. let students: [(name: String, score: Int)] = [ ("Alice", 75), ("Bob", 51), ("Carol", 84), ("Dave", 93), ("Eve", 50) ] let bestStudent = students.sorted { $0.score < $1.score }.last?.name ?? "" var bestStudent = "" var maxScore = 0 for student in students { if student.score > maxScore { bestStudent = student.name maxScore = student.score } }
15. let students: [(name: String, score: Int)] = [ ("Alice", 75), ("Bob", 51), ("Carol", 84), ("Dave", 93), ("Eve", 50) ] let bestStudent = students.sorted { $0.score < $1.score }.last?.name ?? "" var maxScore = 0 for student in students { if student.score > maxScore { bestStudent = student.name maxScore = student.score } }
16. let students: [(name: String, score: Int)] = [ ("Alice", 75), ("Bob", 51), ("Carol", 84), ("Dave", 93), ("Eve", 50) ] let bestStudent = students.max { $0.score < $1.score }?.name ?? "" var maxScore = 0 for student in students { if student.score > maxScore { bestStudent = student.name maxScore = student.score } } max(by:) / min(by:)
17. https://developer.apple.com/documentation/swift/array# Selecting-Elements Array https://developer.apple.com/documentation/swift/array# Excluding-Elements Selecting & Excluding
18. prefix(_:) / suffix(_:) / dropFirst(_:) / dropLast(_:) let chars: [Character] = ["A", "B", "C", "D", "E", "F"] print(chars.prefix(2)) // Prints ArraySlice(["A", "B"]) print(chars.suffix(2)) // Prints ArraySlice(["E", "F"]) print(chars.dropFirst(2)) // Prints ArraySlice(["C", "D", "E", "F"]) print(chars.dropLast(2)) // Prints ArraySlice(["A", "B", "C", "D"])
19. extension Array { subscript(safe index: Int) -> Element? { self.dropFirst(index).first guard index >= 0, index < count else { return nil } return self[index] } } print(chars[safe: 2]) // Prints Optional("C") print(chars[safe: 6]) // Prints nil
20. extension Array { subscript(safe index: Int) -> Element? { self.dropFirst(index).first guard index >= 0, index < count else { return nil } return self[index] } } print(chars[safe: 2]) // Prints Optional("C") print(chars[safe: 6]) // Prints nil
21. 0 1 2 3 4 5 A B C D E F dropFirst(2) extension Array { subscript(safe index: Int) -> Element? { self.dropFirst(index).first guard index >= 0, index < count else { return nil } return self[index] } } print(chars[safe: 2]) // Prints Optional("C") print(chars[safe: 6]) // Prints nil
22. 0 1 2 3 4 5 A B C D E F dropFirst(6) extension Array { subscript(safe index: Int) -> Element? { self.dropFirst(index).first guard index >= 0, index < count else { return nil } return self[index] } } print(chars[safe: 2]) // Prints Optional("C") print(chars[safe: 6]) // Prints nil F
23. Swift Array / filter(_:) / map(_:) / flatMap(_:) compactMap(_:) / reduce(_:_:) / sorted(by:) / reversed() contains(where:) / allSatisfy(_:) / min(by:) / max(by:) prefix(_:) / prefix(through:) / prefix(upTo:) prefix(while:) / suffix(_:) / suffix(from:) / dropFirst(_:) dropLast(_:) / drop(while:) / removeAll(where:) first(where:) / firstIndex(where:) / last(where:) lastIndex(where:) / forEach(_:) / enumerated() partition(by:)
24. Swift Algorithms https://developer.apple.com/videos/play/wwdc2021/10256/
25. import Algorithms let x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] for i in 1 ..< x.count { print(x[i - 1], x[i]) } // Prints (0, 1) // Prints (1, 2) // Prints (2, 3) // Prints (3, 4) // Prints (4, 5) // Prints (5, 6) 2 3 4 5 6 7 8 9 0 1 1 ..< x.count
26. import Algorithms let x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] for (prev, next) in x.adjacentPairs() { print(prev, next) } // Prints (0, 1) // Prints (1, 2) // Prints (2, 3) // Prints (3, 4) // Prints (4, 5) // Prints (5, 6) 8 9 x.adjacentPairs()
27. import Algorithms let x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] for window in x.windows(ofCount: 3) { print(window) } // Prints ArraySlice([0, 1, 2]) // Prints ArraySlice([1, 2, 3]) // Prints ArraySlice([2, 3, 4]) // Prints ArraySlice([3, 4, 5]) // Prints ArraySlice([4, 5, 6]) // Prints ArraySlice([5, 6, 7]) x.windows(ofCount: 3) 2 3 4 5 6 7 8 9 0 1
28. import Algorithms let x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] for chunk in x.chunks(ofCount: 3) { print(chunk) } // Prints ArraySlice([0, 1, 2]) // Prints ArraySlice([3, 4, 5]) // Prints ArraySlice([6, 7, 8]) // Prints ArraySlice([9]) x.chunks(ofCount: 3) 2 3 4 5 6 0 1 7 8 9
29. import Algorithms let x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] for chunk in x.evenlyChunked(in: 4) { print(chunk) } // Prints ArraySlice([0, 1, 2]) // Prints ArraySlice([3, 4, 5]) // Prints ArraySlice([6, 7]) // Prints ArraySlice([8, 9]) x.evenlyChunked(in: 4) 2 3 4 5 6 0 1 7 8 9
30. 7/5 4:54 👧 7/5 4:55 👧 7/5 5:03 👧 7/5 7:06 👦 7/5 7:38 👦 7/5 7:38 👦 7/7 9:41 👦 7/7 9:41 👧 7/7 9:41 👧 7/7 9:42 👧 import Algorithms struct Message { let date: Date let sender: String let text: String } ForEach(messages.chunked(by: { $0.sender == $1.sender })) { chunk in ForEach(messages) { message in MessageView(message) }
31. 👧 👧 👦 import Algorithms struct Message { let date: Date let sender: String let text: String } ForEach ForEach(messages.chunked(by: { $0.sender == $1.sender })) { chunk in ForEach(messages) { message in Section { ForEach(chunk) { message in MessageView(message) } } } 7/5 4:54 👧 7/5 4:55 👧 7/5 5:03 👧 7/5 7:06 👦 7/5 7:38 👦 7/5 7:38 👦 7/7 9:41 👦 7/7 9:41 👧 7/7 9:41 👧 7/7 9:42 👧 ForEach(messages.chunked(by: { $0.sender == $1.sender })) { chunk in
32. import Algorithms struct Message { let date: Date let sender: String let text: String } ForEach(messages.chunked(on: \.sender), id: \.1) { sender, chunk in ForEach(messages.chunked(by: { $0.sender == $1.sender })) { chunk in Section { ForEach(chunk) { message in MessageView(message) } } header: { Text(sender) } } 👧 👧 👦 7/5 4:54 … 7/5 4:55 … 7/5 5:03 … 7/5 7:06 … 7/5 7:38 … 7/5 7:38 … 7/7 9:41 … 7/7 9:41 … 7/7 9:41 … 7/7 9:42 … ForEach(messages.chunked(on: \.sender), id: \.1) { sender, chunk in } header: { Text(sender) } sender,
33. let senders = messages.map(\.sender).uniqued() // [ , ] let senderMessages = messages.uniqued(on: \.sender) // [ , ] 👧 👦 7/5 4:54 👧 7/5 7:06 👦 uniqued() / uniqued(on:)
34. let messagesBySender: [String: [Message]] = messages.grouped(by: \.sender) // [ : ]. , : ] grouped(by:) 7/5 4:54 👧 7/5 4:55 👧 7/5 5:03 👧 7/5 7:06 👦 7/5 7:38 👦 7/5 7:38 👦 7/7 9:41 👦 7/7 9:41 👧 7/7 9:41 👧 7/7 9:42 👧 👧 👦
35. grouped(by:) https://github.com/apple/swift-algorithms/blob/main/Sources/Algorithms/Grouped.swift
36. let currentUser = "👦" let selfMessages = messages.filter { $0.sender == currentUser } let otherMessages = messages.filter { $0.sender != currentUser }
37. let currentUser = "👦" let (otherMessages, selfMessages) = messages.partitioned { $0.sender == currentUser } partitioned(by:)
38. let date = DateComponents(calendar: .current, month: 7, day: 7).date! let index = messages.partitioningIndex { $0.date > date } print(messages[index...]) // Prints ArraySlice([ , , , ]) partitioningIndex(where:) 7/7 9:41 👦 7/7 9:41 👧 7/7 9:41 👧 7/7 9:42 👧 𝑂(log 𝑛)
39. func sqrt(x: Int) -> Int { (0 ..< x) .partitioningIndex { $0 * $0 >= x } } func sqrt(x: Int) -> Int { var l = 0 var r = x while l <= r { let m = (l + r) / 2 if m * m >= x { r = m - 1 } else { l = m + 1 } } return l } Scenario Compute ceiling of √𝒙 with Binary Search (Find the smallest integer ≥ √𝒙) √𝟏 = 𝟏 √𝟒 = 𝟐 √𝟏𝟎 ≈ 𝟒
40. Swift Algorithms / adjacentPairs() / chain(_:_:) / chunked(by:) / chunked(on:) chunks(ofCount:) / combinations() / combinations(ofCount:) / compacted() cycled() / cycled(times:) / firstNonNil(by:) / interspersed(with:) / joined(by:) max(count:) / max(count:sortedBy:) / min(count:) / min(count:sortedBy:) minAndMax() / minAndMax(by:) / partitioningIndex(where:) / permutations() permutations(ofCount:) / product(_:_:) / randomSample(count:) randomStableSample(count:) / reductions(_:) / reductions(_:_:) reductions(into:_:) / rotate(toStartAt:) / rotate(subrange:toStartAt:) split(whereSeperator:) / split(seperator:) / stablePartition(by:) stablePartition(subrange:by:) / striding(by:) / suffix(while:) / trimming(while:) trimmingPrefix(while:) / trimmingSuffix(while:) / uniquedPermutations() uniquedPermutations(ofCount:) / uniqued() / uniqued(on:) / windows(ofCount:) https://github.com/apple/swift-algorithms
41. Scenario Given an array of scores, count how many scores are above the average func count(scores: [Int]) -> Int { let average = scores.reduce(0, +) / scores.count return scores.count { $0 > average } }
42. Scenario Given an array of scores, count how many scores are above the average func count(scores: [Int]) -> Int { scores.count { $0 > scores.reduce(0, +) / scores.count } }
43. Capture List Given an array of scores, count how many scores are above the average func count(scores: [Int]) -> Int { scores.count { [average = scores.reduce(0, +) / scores.count] in $0 > average } }
44. @State private var pulse: Bool = false var body: some View { Text(message.text) .visualEffect { [pulse] content, _ in content .blur(radius: pulse ? 2 : 0) } } Capture List Given an array of scores, count how many scores are above the average Prevent Data Races Prevent Retain Cycle [pulse] self.onEvent = { [weak self] in self?.navigationController?.popViewController(animated: true) } [weak self]
45. @State private var pulse: Bool = false var body: some View { let pulse = pulse Text(message.text) .visualEffect { content, _ in content .blur(radius: pulse ? 2 : 0) } } Capture List Given an array of scores, count how many scores are above the average Prevent Data Races Prevent Retain Cycle let pulse = pulse weak var weakSelf = self self.onEvent = { weakSelf?.navigationController?.popViewController(animated: true) } weak var weakSelf = self
46. func diff(scores: [Int]) -> Int { guard let maxPassingScore = scores.filter({ $0 >= 60 }).max() else { return nil } return 100 - maxPassingScore } Scenario Calculate the difference between the highest passing score (≥ 60) and 100 If no score is passing, return nil
47. func diff(scores: [Int]) -> Int { scores .filter { $0 >= 60 } .max() .map { (maxPassingScore: Int) -> Int in 100 - maxPassingScore } } Optional.map(_:) Calculate the difference between the highest passing score (≥ 60) and 100 If no score is passing, return nil .map { (maxPassingScore: Int) -> Int in 100 - maxPassingScore }
48. @IBOutlet weak var nameLabel: UILabel! @IBOutlet weak var messageLabel: UILabel! @IBOutlet weak var dateLabel: UILabel! func setupUI(message: Message) { nameLabel.isHidden = message.sender.isEmpty nameLabel.text = message.sender messageLabel.isHidden = message.text.isEmpty messageLabel.text = message.text dateLabel.text = message.date.formatted(date: .abbreviated, time: .standard) dateLabel.accessibilityLabel = message.date.formatted(date: .long, time: .standard) } 7/5 4:54 👧 Optional.map(_:)
49. @IBOutlet weak var nameLabel: UILabel! @IBOutlet weak var messageLabel: UILabel! @IBOutlet weak var dateLabel: UILabel! func setupUI(message: Message) { // Setup name label nameLabel.isHidden = message.sender.isEmpty nameLabel.text = message.sender // Setup message label messageLabel.isHidden = message.text.isEmpty messageLabel.text = message.text // Setup date label dateLabel.text = message.date.formatted(date: .abbreviated, time: .standard) dateLabel.accessibilityLabel = message.date.formatted(date: .long, time: .standard) } 7/5 4:54 👧 Optional.map(_:)
50. @IBOutlet weak var nameLabel: UILabel! @IBOutlet weak var messageLabel: UILabel! @IBOutlet weak var dateLabel: UILabel! func setupUI(message: Message) { nameLabel.map { $0.isHidden = message.sender.isEmpty $0.text = message.sender } messageLabel.map { $0.isHidden = message.text.isEmpty $0.text = message.text } dateLabel.map { $0.text = message.date.formatted(date: .abbreviated, time: .standard) $0.accessibilityLabel = message.date.formatted(date: .long, time: .standard) } } Optional.map(_:) 7/5 4:54 👧
51. Wrap up Array Higher Order Functions Swift Algorithms package Use Capture List or Optional.map for 1-liner Higher Order Functions Swift Algorithms Capture List Optional.map
52. Next steps Introduce Swift Algorithms to improve your code Write your own 1-liner Enjoy the Follow「iamhands0me」on
53. Two Sum Given an array of integers nums and an integer target Return indices of the two numbers such that they add up to target func twoSum(_ nums: [Int], _ target: Int) -> [Int] { nums .indices .combinations(ofCount: 2) .first { nums[$0[0]] + nums[$0[1]] == target } ?? [] } nums target target
54. Two Sum Given an array of integers nums and an integer target Return indices of the two numbers such that they add up to target func twoSum(_ nums: [Int], _ target: Int) -> [Int] { nums .indices .firstNonNil { [group = nums.indices.grouped { nums[$0] }] i in group[target - nums[i], default: []] .first { $0 != i } .map { j in [i, j] } } ?? [] } nums target target