The Great iOS Concurrency Bake-Off - Swift Usergroup Netherlands, Amsterdam, February 2019

An Instant Replay™ of my concurrency talk from mobOS!

Abstract:
Callback Hell is a problem affecting developers of all stripes trying to write asynchronous code that's easy to follow. iOS developers don't yet have much in the way of built-in options to reduce callback hell, but there are several libraries which purport to help. In this session, you'll get a look at what problems are being solved by RxSwift and PromiseKit, as well as a look at an intriguing functional technique to avoid callback hell without libraries. And you'll learn more about how to answer the question: Which of these hammers is the most appropriate for my particular nail?

I will also make a ton of references to the Great British Bake Off, which you should watch because it is delightful.

Code:
https://github.com/designatednerd/OperationComparison

Original slides (they're pretty damned similar):
https://speakerdeck.com/designatednerd/the-great-ios-concurrency-bake-off-mobos-cluj-napoca-romania-february-2019

Transcript

1. The Great iOS Concurrency ! " Bake-Off ! Swift Usergroup NL ! | Amsterdam | February 2019 @DesignatedNerd | bakkenbaeck.no | justhum.com
2. What is Concurrency?
3. Concurrency vs. Parallelism
4. Metaphor Time!
26. Concurrency: "One thing should do these tasks at as close to the same time as possible."
35. Parallelism: "Many things should do all these identical mini-tasks at the same time."
42. !
43. Taking the result of an asynchronous function
44. Taking the result of an asynchronous function Giving it to another asynchronous function
45. Taking the result of an asynchronous function Giving it to another asynchronous function (and another and another)
46. The Problem: ! Callback Hell
47. Teh Codez! https://github.com/designatednerd/ OperationComparison
48. As a user, I want to see a profile picture when viewing a profile.
49. As a developer, I want a list of profiles with icons to not drop frames when scrolling.
50. User Data -> Icon Image -> Resized Icon Image static func fetchUser(failureCompletion: @escaping (Error) -> Void, successCompletion: @escaping (User) -> Void) static func fetchImage(for user: User, failureCompletion: @escaping (Swift.Error) -> Void, successCompletion: @escaping (UIImage) -> Void) static func resizeImage(_ image: UIImage, to size: CGSize, failureCompletion: @escaping (Swift.Error) -> Void, successCompletion: @escaping (UIImage) -> Void)
51. Not Horrible... self.activityIndicator.startAnimating() FakeAPI.fetchUser(failureCompletion: { [weak self] error in guard let self = self else { return } self.activityIndicator.stopAnimating() self.operationLabel.text = "Error fetching user: \(error)" }, successCompletion: { [weak self] user in guard let self = self else { return } self.operationLabel.text = "Fetching image..." })
52. Not ideal... self.activityIndicator.startAnimating() FakeAPI.fetchUser(failureCompletion: { [weak self] error in guard let self = self else { return } self.activityIndicator.stopAnimating() self.operationLabel.text = "Error fetching user: \(error)" }, successCompletion: { [weak self] user in guard let self = self else { return } self.operationLabel.text = "Fetching image..." RealAPI.fetchImage(for: user, failureCompletion: { [weak self] error in guard let self = self else { return } self.activityIndicator.stopAnimating() self.operationLabel.text = "Error fetching image: \(error)" }, successCompletion: { [weak self] image in guard let self = self else { return } self.operationLabel.text = "Resizing image..." }) })
53. ...Does anyone have a ? self.activityIndicator.startAnimating() FakeAPI.fetchUser(failureCompletion: { [weak self] error in guard let self = self else { return } self.activityIndicator.stopAnimating() self.operationLabel.text = "Error fetching user: \(error)" }, successCompletion: { [weak self] user in guard let self = self else { return } self.operationLabel.text = "Fetching image..." RealAPI.fetchImage(for: user, failureCompletion: { [weak self] error in guard let self = self else { return } self.activityIndicator.stopAnimating() self.operationLabel.text = "Error fetching image: \(error)" }, successCompletion: { [weak self] image in guard let self = self else { return } self.operationLabel.text = "Resizing image..." ImageResizer.resizeImage(image, to: self.imageView.frame.size, failureCompletion: { [weak self] error in guard let self = self else { return } self.activityIndicator.stopAnimating() self.operationLabel.text = "Error resizing image: \(error)" }, successCompletion: { [weak self] resizedImage in guard let self = self else { return } self.activityIndicator.stopAnimating() self.imageView.image = resizedImage self.operationLabel.text = "Complete in \(self.formattedSecondsSince(start))!" }) }) })
54. ¯\_(ϑ)_/¯ Avoid UI interaction and don't care about retain cycles!
55. ¯\_(ϑ)_/¯ Avoid UI interaction and don't care about retain cycles!* * - not recommended
56. FakeAPI.fetchUser(failureCompletion: { error in debugPrint("Error fetching user: \(error)") }, successCompletion: { user in RealAPI.fetchImage(for: user, failureCompletion: { error in debugPrint("Error fetching image: \(error)") }, successCompletion: { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size, failureCompletion: { error in debugPrint("Error resizing image: \(error)") }, successCompletion: { resizedImage in self.imageView.image = resizedImage debugPrint("Complete in \(self.formattedSecondsSince(start))!" }) }) })
57. Think Indent Different
58. FakeAPI.fetchUser( errorCompletion: { error in debugPrint("Error fetching user: \(error)") }, successCompletion: { user in RealAPI.fetchImage( for: user, failureCompletion: { error in debugPrint("Error fetching image: \(error)") }, successCompletion: { image in ImageResizer.resizeImage( image, to: self.imageView.frame.size, failureCompletion: { error in debugPrint("Error resizing image: \(error)") }, successCompletion: { resizedImage in self.imageView.image = resizedImage debugPrint("Complete in \(self.formattedSecondsSince(start))!" }) }) })
59. Try to break it a p a r t
60. private func fetchUser() { FakeAPI.fetchUser( failureCompletion: { error in debugPrint("Error fetching user: \(error)") }, successCompletion: { user in self.fetchImage(for: user) }) } private func fetchImage(for user: User) { RealAPI.fetchImage( for: user, failureCompletion: { error in debugPrint("Error fetching image: \(error)") }, successCompletion: { image in self.resizeImage(image, to: self.imageView.frame.size) }) } private func resizeImage(_ image: UIImage, to size: CGSize) { ImageResizer.resizeImage( image, to: self.imageView.frame.size, failureCompletion: { error in debugPrint("Error resizing image: \(error)") }, successCompletion: { [weak self] resizedImage in guard let self = self else { return } self.imageView.image = resizedImage debugPrint("Complete in \(self.formattedSecondsSince(start))!") }) }
61. The problem: Dependent functions
62. private func fetchUser() { FakeAPI.fetchUser( failureCompletion: { error in debugPrint("Error fetching user: \(error)") }, successCompletion: { user in self.fetchImage(for: user) }) } private func fetchImage(for user: User) { RealAPI.fetchImage( for: user, failureCompletion: { error in debugPrint("Error fetching image: \(error)") }, successCompletion: { image in self.resizeImage(image, to: self.imageView.frame.size) }) } private func resizeImage(_ image: UIImage, to size: CGSize) { ImageResizer.resizeImage( image, to: self.imageView.frame.size, failureCompletion: { error in debugPrint("Error resizing image: \(error)") }, successCompletion: { [weak self] resizedImage in guard let self = self else { return } self.imageView.image = resizedImage debugPrint("Complete in \(self.formattedSecondsSince(start))!") }) }
63. private func fetchUser() { FakeAPI.fetchUser( failureCompletion: { error in debugPrint("Error fetching user: \(error)") }, successCompletion: { user in self.fetchImage(for: user) }) } private func fetchImage(for user: User) { RealAPI.fetchImage( for: user, failureCompletion: { error in debugPrint("Error fetching image: \(error)") }, successCompletion: { image in self.resizeImage(image, to: self.imageView.frame.size) }) } private func resizeImage(_ image: UIImage, to size: CGSize) { ImageResizer.resizeImage( image, to: self.imageView.frame.size, failureCompletion: { error in debugPrint("Error resizing image: \(error)") }, successCompletion: { [weak self] resizedImage in guard let self = self else { return } self.imageView.image = resizedImage debugPrint("Complete in \(self.formattedSecondsSince(start))!") }) }
64. FakeAPI.fetchUser( errorCompletion: { error in debugPrint("Error fetching user: \(error)") }, successCompletion: { user in RealAPI.fetchImage( for: user, failureCompletion: { error in debugPrint("Error fetching image: \(error)") }, successCompletion: { image in ImageResizer.resizeImage( image, to: self.imageView.frame.size, failureCompletion: { error in debugPrint("Error resizing image: \(error)") }, successCompletion: { resizedImage in self.imageView.image = resizedImage debugPrint("Complete in \(self.formattedSecondsSince(start))!" }) }) })
65. A slight help: The Result Type
66. ! Swift 5.0 https://github.com/apple/swift/blob/master/ stdlib/public/core/ Result.swift
67. Result.Swift public enum Result<Success, Failure: Error> { /// A success, storing a `Success` value. case success(Success) /// A failure, storing a `Failure` value. case failure(Failure) }
68. User Data -> Icon Image -> Resized Icon Image static func fetchUser(failureCompletion: @escaping (Error) -> Void, successCompletion: @escaping (User) -> Void) static func fetchImage(for user: User, failureCompletion: @escaping (Swift.Error) -> Void, successCompletion: @escaping (UIImage) -> Void) static func resizeImage(_ image: UIImage, to size: CGSize, failureCompletion: @escaping (Swift.Error) -> Void, successCompletion: @escaping (UIImage) -> Void)
69. User Data -> Icon Image -> Resized Icon Image static func fetchUser(completion: @escaping (Result<User, Error>) -> Void) static func fetchImage(for user: User, completion: @escaping (Result<UIImage, Error>) -> Void) static func resizeImage(_ image: UIImage, to size: CGSize, failureCompletion: @escaping (Result<UIImage, Error>) -> Void)
70. FakeAPI.fetchUser { userResult in switch userResult { case .success(let user): RealAPI.fetchImage(for: user) { imageResult in switch imageResult { case .success(let image): ImageResizer.resizeImage(image, to: self.imageView.frame.size) { resizedImageResult in switch resizedImageResult { case .success(let resizedImage): self.imageView.image = resizedImage debugPrint("Complete") case .failure(let error): debugPrint("Error resizing image: \(error)") } } case .failure(let error): debugPrint("Error fetching image: \(error)") } } case .failure(let error): debugPrint("Error fetching user: \(error)") } }
71. FakeAPI.fetchUser { userResult in switch userResult { case .success(let user): RealAPI.fetchImage(for: user) { imageResult in switch imageResult { case .success(let image): ImageResizer.resizeImage(image, to: self.imageView.frame.size) { resizedImageResult in switch resizedImageResult { case .success(let resizedImage): self.imageView.image = resizedImage debugPrint("Complete") case .failure(let error): debugPrint("Error resizing image: \(error)") } } case .failure(let error): debugPrint("Error fetching image: \(error)") } } case .failure(let error): debugPrint("Error fetching user: \(error)") } }
72. FakeAPI.fetchUser { userResult in switch userResult { case .success(let user): RealAPI.fetchImage(for: user) { imageResult in switch imageResult { case .success(let image): ImageResizer.resizeImage( image, to: self.imageView.frame.size) { resizedImageResult in switch resizedImageResult { case .success(let resizedImage): self.imageView.image = resizedImage debugPrint("Complete") case .failure(let error): debugPrint("Error resizing image: \(error)") } } case .failure(let error): debugPrint("Error fetching image: \(error)") } } case .failure(let error): debugPrint("Error fetching user: \(error)") } }
73. FakeAPI.fetchUser { userResult in switch userResult { case .success(let user): RealAPI.fetchImage(for: user) { imageResult in switch imageResult { case .success(let image): ImageResizer.resizeImage( image, to: self.imageView.frame.size) { resizedImageResult in switch resizedImageResult { case .success(let resizedImage): self.imageView.image = resizedImage debugPrint("Complete") case .failure(let error): debugPrint("Error resizing image: \(error)") } } case .failure(let error): debugPrint("Error fetching image: \(error)") } } case .failure(let error): debugPrint("Error fetching user: \(error)") } }
74. How do we chain operations which need each others' results clearly?
75. How do we chain operations which need each others' results in an easy-to-follow way?
76. How do we chain operations which need each others' results so we can figure out where something's going wrong?
77. ! " Bake-Off!
81. Three competitors
82. Three competitors (out of way more than three)
86. The Problem: ! Callback Hell
87. Three competitors
88. Three competitors 1. Operator Overloading
89. Three competitors 1. Operator Overloading 2. PromiseKit
90. Three competitors 1. Operator Overloading 2. PromiseKit 3. RxSwift
91. ! Signature Challenge:
92. ! Signature Challenge: Making Code More Readable
93. Competitor #1: Operator Overloading
94. Competitor #1: Operator Overloading "We don't need no stinkin' libraries!"
96. typealias ResultCompletion<T> = (Result<T, Error>) -> Void infix operator -->: MultiplicationPrecedence func --><T,U>(_ firstFunction: @escaping (@escaping ResultCompletion<T>) -> Void, _ secondFunction: @escaping (T, @escaping ResultCompletion<U>) -> Void) -> (@escaping ResultCompletion<U>) -> Void { return { completion in firstFunction { result in switch result { case .success(let item): secondFunction(item) { result2 in completion(result2) } case .error(let error): completion(.error(error)) } } } }
97. typealias ResultCompletion<T> = (Result<T, Error>) -> Void infix operator -->: MultiplicationPrecedence func --><T,U>(_ firstFunction: @escaping (@escaping ResultCompletion<T>) -> Void, _ secondFunction: @escaping (T, @escaping ResultCompletion<U>) -> Void) -> (@escaping ResultCompletion<U>) -> Void { return { completion in firstFunction { result in switch result { case .success(let item): secondFunction(item) { result2 in completion(result2) } case .error(let error): completion(.error(error)) } } } }
98. typealias ResultCompletion<T> = (Result<T, Error>) -> Void infix operator -->: MultiplicationPrecedence func --><T,U>(_ firstFunction: @escaping (@escaping ResultCompletion<T>) -> Void, _ secondFunction: @escaping (T, @escaping ResultCompletion<U>) -> Void) -> (@escaping ResultCompletion<U>) -> Void { return { completion in firstFunction { result in switch result { case .success(let item): secondFunction(item) { result2 in completion(result2) } case .error(let error): completion(.error(error)) } } } }
99. PEMDAS
100. PEMDAS (parentheses, exponents, multiplication, division, addition, subtraction)
101. typealias ResultCompletion<T> = (Result<T, Error>) -> Void infix operator -->: MultiplicationPrecedence func --><T,U>(_ firstFunction: @escaping (@escaping ResultCompletion<T>) -> Void, _ secondFunction: @escaping (T, @escaping ResultCompletion<U>) -> Void) -> (@escaping ResultCompletion<U>) -> Void { return { completion in firstFunction { result in switch result { case .success(let item): secondFunction(item) { result2 in completion(result2) } case .error(let error): completion(.error(error)) } } } }
102. typealias ResultCompletion<T> = (Result<T, Error>) -> Void infix operator -->: MultiplicationPrecedence func --><T,U>(_ firstFunction: @escaping (@escaping ResultCompletion<T>) -> Void, _ secondFunction: @escaping (T, @escaping ResultCompletion<U>) -> Void) -> (@escaping ResultCompletion<U>) -> Void { return { completion in firstFunction { result in switch result { case .success(let item): secondFunction(item) { result2 in completion(result2) } case .error(let error): completion(.error(error)) } } } }
103. typealias ResultCompletion<T> = (Result<T, Error>) -> Void infix operator -->: MultiplicationPrecedence func --><T,U>(_ firstFunction: @escaping (@escaping ResultCompletion<T>) -> Void, _ secondFunction: @escaping (T, @escaping ResultCompletion<U>) -> Void) -> (@escaping ResultCompletion<U>) -> Void { return { completion in firstFunction { result in switch result { case .success(let item): secondFunction(item) { result2 in completion(result2) } case .error(let error): completion(.error(error)) } } } }
104. typealias ResultCompletion<T> = (Result<T, Error>) -> Void infix operator -->: MultiplicationPrecedence func --><T,U>(_ firstFunction: @escaping (@escaping ResultCompletion<T>) -> Void, _ secondFunction: @escaping (T, @escaping ResultCompletion<U>) -> Void) -> (@escaping ResultCompletion<U>) -> Void { return { completion in firstFunction { result in switch result { case .success(let item): secondFunction(item) { result2 in completion(result2) } case .error(let error): completion(.error(error)) } } } }
105. typealias ResultCompletion<T> = (Result<T, Error>) -> Void infix operator -->: MultiplicationPrecedence func --><T,U>(_ firstFunction: @escaping (@escaping ResultCompletion<T>) -> Void, _ secondFunction: @escaping (T, @escaping ResultCompletion<U>) -> Void) -> (@escaping ResultCompletion<U>) -> Void { return { completion in firstFunction { result in switch result { case .success(let item): secondFunction(item) { result2 in completion(result2) } case .error(let error): completion(.error(error)) } } } }
106. User Data -> Icon Image -> Resized Icon Image static func fetchUser(completion: @escaping (Result<User, Error>) -> Void) static func fetchImage(for user: User, completion: @escaping (Result<UIImage, Error>) -> Void) static func resizeImage(_ image: UIImage, to size: CGSize, failureCompletion: @escaping (Result<UIImage, Error>) -> Void)
107. User Data -> Icon Image -> Resized Icon Image static func fetchUser(completion: @escaping (Result<User, Error>) -> Void) static func fetchImage(for user: User, completion: @escaping (Result<UIImage, Error>) -> Void) static func resizeImage(_ image: UIImage, to size: CGSize, failureCompletion: @escaping (Result<UIImage, Error>) -> Void)
108. User Data -> Icon Image -> Resized Icon Image static func fetchUser(completion: @escaping (Result<User, Error>) -> Void) static func fetchImage(for user: User, completion: @escaping (Result<UIImage, Error>) -> Void) static func resizeImage(_ image: UIImage, to size: CGSize, failureCompletion: @escaping (Result<UIImage, Error>) -> Void)
109. ! Wrapper Methods private func resizeImageForImageView(_ image: UIImage, completion: @escaping (Swift.Result<UIImage, Swift.Error>) -> Void) { ImageResizer.resizeImage(image, to: self.imageView.frame.size, completion: completion) }
110. ! Wrapper Methods private func resizeImageForImageView(_ image: UIImage, completion: @escaping (Swift.Result<UIImage, Swift.Error>) -> Void) { self.operationLabel.text = "Resizing image (Custom Operator)..." ImageResizer.resizeImage(image, to: self.imageView.frame.size, completion: completion) } private func fetchUserImage(for user: User, completion: @escaping (Swift.Result<UIImage, Swift.Error>) -> Void) { self.operationLabel.text = "Fetching image (Custom Operator)..." RealAPI.fetchImage(for: user, completion: completion) }
111. self.activityIndicator.startAnimating() let chain = API.fetchUser --> fetchUserImage --> resizeImageForImageView chain { result in self.activityIndicator.stopAnimating() switch result { case .success(let image): self.imageView.image = image self.operationLabel.text = "Complete (Custom Operator)!" case .error(let error): self.operationLabel.text = "Error occurred (Custom Operator): \(error)" } }
112. self.activityIndicator.startAnimating() let chain = API.fetchUser --> fetchUserImage --> resizeImageForImageView chain { result in self.activityIndicator.stopAnimating() switch result { case .success(let image): self.imageView.image = image self.operationLabel.text = "Complete (Custom Operator)!" case .error(let error): self.operationLabel.text = "Error occurred (Custom Operator): \(error)" } }
113. self.activityIndicator.startAnimating() let chain = API.fetchUser --> fetchUserImage --> resizeImageForImageView chain { result in self.activityIndicator.stopAnimating() switch result { case .success(let image): self.imageView.image = image self.operationLabel.text = "Complete (Custom Operator)!" case .error(let error): self.operationLabel.text = "Error occurred (Custom Operator): \(error)" } }
114. typealias ResultCompletion<T> = (Result<T, Error>) -> Void infix operator -->: MultiplicationPrecedence func --><T,U>(_ firstFunction: @escaping (@escaping ResultCompletion<T>) -> Void, _ secondFunction: @escaping (T, @escaping ResultCompletion<U>) -> Void) -> (@escaping ResultCompletion<U>) -> Void { return { completion in firstFunction { result in switch result { case .success(let item): secondFunction(item) { result2 in completion(result2) } case .error(let error): completion(.error(error)) } } } }
115. typealias ResultCompletion<T> = (Result<T, Error>) -> Void infix operator -->: MultiplicationPrecedence func --><T,U>(_ firstFunction: @escaping (@escaping ResultCompletion<T>) -> Void, _ secondFunction: @escaping (T, @escaping ResultCompletion<U>) -> Void) -> (@escaping ResultCompletion<U>) -> Void { return { completion in firstFunction { result in switch result { case .success(let item): secondFunction(item) { result2 in completion(result2) } case .error(let error): completion(.error(error)) } } } }
116. Pro: You Do It Yourself
117. Con: You Do It Yourself
118. Competitor #2: PromiseKit
119. Competitor #2: PromiseKit "OK, fine. Maybe we do need a library."
122. User Data -> Icon Image -> Resized Icon Image static func fetchUser(completion: @escaping (Result<User, Error>) -> Void) static func fetchImage(for user: User, completion: @escaping (Result<UIImage, Error>) -> Void) static func resizeImage(_ image: UIImage, to size: CGSize, failureCompletion: @escaping (Result<UIImage, Error>) -> Void)
123. User Data -> Icon Image -> Resized Icon Image static func fetchUser() -> Promise<User> static func fetchImage(for user: User) -> Promise<Image> static func resizeImage(_ image: UIImage, to size: CGSize) -> Promise<Image>
124. self.activityIndicator.startAnimating() FakeAPI.fetchUser() .then { user in RealAPI.fetchImage(for: user) } .then { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
125. self.activityIndicator.startAnimating() FakeAPI.fetchUser() .then { user in RealAPI.fetchImage(for: user) } .then { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
126. self.activityIndicator.startAnimating() FakeAPI.fetchUser() .then { user in RealAPI.fetchImage(for: user) } .then { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
127. self.activityIndicator.startAnimating() FakeAPI.fetchUser() .then { user in RealAPI.fetchImage(for: user) } .then { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
128. self.activityIndicator.startAnimating() FakeAPI.fetchUser() .then { user in RealAPI.fetchImage(for: user) } .then { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
129. self.activityIndicator.startAnimating() FakeAPI.fetchUser() .then { user in RealAPI.fetchImage(for: user) } .then { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
130. self.activityIndicator.startAnimating() FakeAPI.fetchUser() .then { user in RealAPI.fetchImage(for: user) } .then { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
132. Solution #3: RxSwift
133. Solution #3: RxSwift "Use ALL the libraries!"
134. User Data -> Icon Image -> Resized Icon Image static func fetchUser() -> Promise<User> static func fetchImage(for user: User) -> Promise<Image> static func resizeImage(_ image: UIImage, to size: CGSize) -> Promise<Image>
135. User Data -> Icon Image -> Resized Icon Image static func fetchUser() -> Single<User> static func fetchImage(for user: User) -> Single<Image> static func resizeImage(_ image: UIImage, to size: CGSize) -> Single<Image>
137. Observable
138. Observable "I could get many values from this, until it tells me things are complete or an error has occurred."
139. Single
140. Single "This will either succeed or fail once."
141. FakeAPI.rx.fetchUser() .flatMap { user in RealAPI.rx.fetchImage(for: user) } .flatMap { image in ImageResizer.rx.resizeImage(image, to: self.imageView.frame.size) } .subscribe( onSuccess: { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (RxSwift) in \(self.formattedSecondsSince(start))!" }, onError: { error in self.operationLabel.text = "Error occurred (RxSwift): \(error)" } ) .disposed(by: bag)
142. FakeAPI.rx.fetchUser() .flatMap { user in RealAPI.rx.fetchImage(for: user) } .flatMap { image in ImageResizer.rx.resizeImage(image, to: self.imageView.frame.size) } .subscribe( onSuccess: { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (RxSwift) in \(self.formattedSecondsSince(start))!" }, onError: { error in self.operationLabel.text = "Error occurred (RxSwift): \(error)" } ) .disposed(by: bag)
143. FakeAPI.rx.fetchUser() .flatMap { user in RealAPI.rx.fetchImage(for: user) } .flatMap { image in ImageResizer.rx.resizeImage(image, to: self.imageView.frame.size) } .subscribe( onSuccess: { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (RxSwift) in \(self.formattedSecondsSince(start))!" }, onError: { error in self.operationLabel.text = "Error occurred (RxSwift): \(error)" } ) .disposed(by: bag)
145. FakeAPI.rx.fetchUser() .flatMap { user in RealAPI.rx.fetchImage(for: user) } .flatMap { image in ImageResizer.rx.resizeImage(image, to: self.imageView.frame.size) } .subscribe( onSuccess: { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (RxSwift) in \(self.formattedSecondsSince(start))!" }, onError: { error in self.operationLabel.text = "Error occurred (RxSwift): \(error)" } ) .disposed(by: bag)
146. FakeAPI.rx.fetchUser() .flatMap { user in RealAPI.rx.fetchImage(for: user) } .flatMap { image in ImageResizer.rx.resizeImage(image, to: self.imageView.frame.size) } .subscribe( onSuccess: { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (RxSwift) in \(self.formattedSecondsSince(start))!" }, onError: { error in self.operationLabel.text = "Error occurred (RxSwift): \(error)" } ) .disposed(by: bag)
147. FakeAPI.rx.fetchUser() .flatMap { user in RealAPI.rx.fetchImage(for: user) } .flatMap { image in ImageResizer.rx.resizeImage(image, to: self.imageView.frame.size) } .subscribe( onSuccess: { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (RxSwift) in \(self.formattedSecondsSince(start))!" }, onError: { error in self.operationLabel.text = "Error occurred (RxSwift): \(error)" } ) .disposed(by: bag)
149. ! Technical Challenge:
150. ! Technical Challenge: Handling Threading
151. Operator Overloading private func fetchUserImage(for user: User, completion: @escaping (Result<UIImage>) -> Void) { self.operationLabel.text = "Fetching image (Custom Operator)..." API.fetchImage(for: user, completion: completion) }
152. Operator Overloading private func fetchUserImage(for user: User, completion: @escaping (Result<UIImage>) -> Void) { self.operationLabel.text = "Fetching image (Custom Operator)..." DispatchQueue.global(qos: .background).async { API.fetchImage(for: user, completion: completion) } }
153. Operator Overloading private func fetchUserImage(for user: User, completion: @escaping (Result<UIImage>) -> Void) { self.operationLabel.text = "Fetching image (Custom Operator)..." DispatchQueue.global(qos: .background).async { API.fetchImage(for: user, completion: completion) } }
154. Operator Overloading private func fetchUserImage(for user: User, completion: @escaping (Result<UIImage>) -> Void) { self.operationLabel.text = "Fetching image (Custom Operator)..." DispatchQueue.global(qos: .background).async { API.fetchImage(for: user, completion: completion) } }
156. PromiseKit FakeAPI.fetchUser() .then { user in RealAPI.fetchImage(for: user) } .then { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
157. PromiseKit FakeAPI.fetchUser() .then(on: .global(qos: .background)) { user in RealAPI.fetchImage(for: user) } .then(on: .global(qos: .background)) { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
158. PromiseKit FakeAPI.fetchUser() .then(on: .global(qos: .background)) { user in RealAPI.fetchImage(for: user) } .then(on: .global(qos: .background)) { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
159. PromiseKit FakeAPI.fetchUser() .then(on: .global(qos: .background)) { user in RealAPI.fetchImage(for: user) } .then(on: .global(qos: .background)) { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
160. PromiseKit 6
161. PromiseKit 6
162. PromiseKit 6
163. PromiseKit 6
164. PromiseKit 6
165. PromiseKit 6
168. PromiseKit 6
169. PromiseKit FakeAPI.fetchUser() .then(on: .global(qos: .background)) { user in RealAPI.fetchImage(for: user) } .map { image in (image, self.imageView.frame.size) } .then(on: .global(qos: .background)) { tuple in ImageResizer.resizeImage(tuple.0, to: tuple.1) } .then(on: .global(qos: .background)) { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
170. PromiseKit FakeAPI.fetchUser() .then(on: .global(qos: .background)) { user in RealAPI.fetchImage(for: user) } .map { image in (image, self.imageView.frame.size) } .then(on: .global(qos: .background)) { tuple in ImageResizer.resizeImage(tuple.0, to: tuple.1) } .then(on: .global(qos: .background)) { image in ImageResizer.resizeImage(image, to: self.imageView.frame.size) } .ensure { self.activityIndicator.stopAnimating() } .done { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (PromiseKit)!" } .catch { [weak self] error in self?.operationLabel.text = "Error occurred (PromiseKit): \(error)" }
171. RxSwift:
172. RxSwift: ! Scheduler
173. It's not a queue!
174. It's not a queue! (it's just way easier to think of it as one)
175. observeOn: tell me what happened here
176. RxSwift FakeAPI.rx.fetchUser() .flatMap { user in RealAPI.rx.fetchImage(for: user) } .flatMap { image in ImageResizer.rx.resizeImage(image, to: self.imageView.frame.size) } .subscribe( onSuccess: { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (RxSwift) in \(self.formattedSecondsSince(start))!" }, onError: { error in self.operationLabel.text = "Error occurred (RxSwift): \(error)" } ) .disposed(by: bag)
177. RxSwift FakeAPI.rx.fetchUser() .flatMap { user in RealAPI.rx.fetchImage(for: user) } .flatMap { image in ImageResizer.rx.resizeImage(image, to: self.imageView.frame.size) } .observeOn(MainScheduler.instance) .subscribe( onSuccess: { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (RxSwift) in \(self.formattedSecondsSince(start))!" }, onError: { error in self.operationLabel.text = "Error occurred (RxSwift): \(error)" } ) .disposed(by: bag)
178. RxSwift FakeAPI.rx.fetchUser() .flatMap { user in RealAPI.rx.fetchImage(for: user) } .flatMap { image in ImageResizer.rx.resizeImage(image, to: self.imageView.frame.size) } .observeOn(MainScheduler.instance) .subscribe( onSuccess: { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (RxSwift) in \(self.formattedSecondsSince(start))!" }, onError: { error in self.operationLabel.text = "Error occurred (RxSwift): \(error)" } ) .disposed(by: bag)
179. subscribeOn: actually do stuff here
180. RxSwift FakeAPI.rx.fetchUser() .flatMap { user in RealAPI.rx.fetchImage(for: user) } .flatMap { image in ImageResizer.rx.resizeImage(image, to: self.imageView.frame.size) } .subscribeOn(ConcurrentDispatchQueueScheduler(qos: .background)) .observeOn(MainScheduler.instance) .subscribe( onSuccess: { resizedImage in self.imageView.image = resizedImage self.operationLabel.text = "Complete (RxSwift) in \(self.formattedSecondsSince(start))!" }, onError: { error in self.operationLabel.text = "Error occurred (RxSwift): \(error)" } ) .disposed(by: bag)
182. Operator overloading: Hard mode
183. PromiseKit: Perform on a queue you specify Call back on a pre-defined queue
184. RxSwift: Always specify where to do stuff Always specify where to call back
185. ! Show-Stopper Challenge:
186. ! Show-Stopper Challenge: Multi-Function Concurrency
187. Two functions at the same time Do something with both results
188. Operator Overloading
189. Operator Overloading
191. PromiseKit: Same Type let userPromise1 = FakeAPI.fetchUser() let userPromise2 = FakeAPI.fetchUser() when(fulfilled: [userPromise1, userPromise2]) .done { users in debugPrint("Users: \(users)") } .catch { error in debugPrint("Error: \(error)") }
192. PromiseKit: Same Type let userPromise1 = FakeAPI.fetchUser() let userPromise2 = FakeAPI.fetchUser() when(fulfilled: [userPromise1, userPromise2]) .done { users in debugPrint("Users: \(users)") } .catch { error in debugPrint("Error: \(error)") }
193. PromiseKit: Same Type let userPromise1 = FakeAPI.fetchUser() let userPromise2 = FakeAPI.fetchUser() when(fulfilled: [userPromise1, userPromise2]) .done { users in debugPrint("Users: \(users)") } .catch { error in debugPrint("Error: \(error)") }
194. PromiseKit: Same Type let userPromise1 = FakeAPI.fetchUser() let userPromise2 = FakeAPI.fetchUser() when(fulfilled: userPromise1, userPromise2) .done { user1, user2 in debugPrint("User1: \(user1), User2: \(user2)") } .catch { error in debugPrint("Error: \(error)") }
195. PromiseKit: Same Type let userPromise1 = FakeAPI.fetchUser() let userPromise2 = FakeAPI.fetchUser() when(fulfilled: userPromise1, userPromise2) .done { user1, user2 in debugPrint("User1: \(user1), User2: \(user2)") } .catch { error in debugPrint("Error: \(error)") }
196. PromiseKit: Different Types let userPromise1 = FakeAPI.fetchUser() let imagePromise = ImageResizer.resizeImage(UIImage(), to: self.imageView.frame.size) when(fulfilled: userPromise1, imagePromise) .done { user, image in debugPrint("User: \(user), image: \(image)") } .catch { error in debugPrint("Error: \(error)") }
197. PromiseKit: Different Types let userPromise1 = FakeAPI.fetchUser() let imagePromise = ImageResizer.resizeImage(UIImage(), to: self.imageView.frame.size) when(fulfilled: userPromise1, imagePromise) .done { user, image in debugPrint("User: \(user), image: \(image)") } .catch { error in debugPrint("Error: \(error)") }
198. PromiseKit: Different Types let userPromise1 = FakeAPI.fetchUser() let imagePromise = ImageResizer.resizeImage(UIImage(), to: self.imageView.frame.size) when(fulfilled: userPromise1, imagePromise) .done { user, image in debugPrint("User: \(user), image: \(image)") } .catch { error in debugPrint("Error: \(error)") }
201. RxSwift
203. Rx Marble Diagrams
204. RxSwift
205. RxSwift
206. RxSwift
207. RxSwift
208. RxSwift
212. JUST PICK ONE!
213. ! PromiseKit
215. ! PromiseKit FOR ME
217. ! Killing flies with a sledgehammer
218. Sometimes you need a sledgehammer
219. Most of the time you only need a fly swatter
220. Obligatory Summary Slide
221. Obligatory Summary Slide → Harder concurrency is it looks than.
222. Obligatory Summary Slide → Concurrency is harder than it looks.
223. Obligatory Summary Slide → Concurrency is harder than it looks. → You can try to handle it yourself, but it's going to be a difficult time sink.
224. Obligatory Summary Slide → Concurrency is harder than it looks. → You can try to handle it yourself, but it's going to be a difficult time sink. → PromiseKit is great for most concurrency handling and readability
225. Obligatory Summary Slide → Concurrency is harder than it looks. → You can try to handle it yourself, but it's going to be a difficult time sink. → PromiseKit is great for most concurrency handling and readability → RxSwift is a giant hammer...but sometimes you need a giant hammer.
227. Choose Wisely
228. Links! → Vincent Pradeilles' Function Composition Talk https://vimeo.com/292702159 → John Sundell's Tasks post https://www.swiftbysundell.com/posts/task-based- concurrency-in-swift → RxMarbles Visualization https://rxmarbles.com
229. ! The Future! → Chris Lattner's Concurrency Manifesto https://gist.github.com/lattner/ 31ed37682ef1576b16bca1432ea9f782 → Kotlin Coroutines: Async/Await + More https://kotlinlang.org/docs/reference/coroutines- overview.html