Introduction to Functional-Reactive Programming

A gentle introduction to Functional-Reactive Programming (FRP).

Includes short intro to Functional Programming (FP), which actually is the foundation of FRP.

Transcript

1. Grzegorz Dyrda Geeky Devs Studio Introduction to Functional-Reactive Programming
2. Grzegorz Dyrda Geeky Devs Studio Introduction to Functional-Reactive Programming
3. Grzegorz Dyrda Geeky Devs Studio Introduction to Functional-Reactive Programming
4. Grzegorz Dyrda Geeky Devs Studio Introduction to Functional-Reactive Programming
5. Functional-Reactive Programming
6. Why? Why do I need to learn another technology?
7. –Bill Gates, 1981 “Nobody will ever need
 more than 640k of RAM”
8. What does the Fox say?
9. What does the Market say?
10. What does the Market say? • Java 9 + Reactive Streams (JEP 266) • Spring Web Reactive (WebFlux) • Angular 2+, Cycle.js • Android Architecture Components, Room, Retrofit, Realm, …
11. Functional-Reactive
12. Functional + Reactive
13. Functional + Reactive
14. Functional + Reactive
15. Functional + Time
16. Functional + Threads
17. Functional + Asynchronous
18. Functional + Asynchronous Concurrency
19. Functional + Asynchronous
20. Functional + Asynchronous
21. Functional
22. You cannot understand Functional-Reactive programming, if you don’t understand Functional programming.
23. What is Functional Programming?
24. Functional Programming Programming style in which we avoid sharing state and data mutation, in favor of composing functions and passing data from one to another.
25. Functional Programming …is about moving from
 the imperative
 to declarative style.
26. Language Support
27. • Functions as first-class citizens • Higher-order functions • Lambda expressions • Immutable data types • Functions are closures Language Support JAVA 8+ APPROVED
28. Example
29. Client says: “Make a sum of all our prices
 that are higher than $20,
 discounted by 10%” Example
30. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example
31. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example var sum = 0.0 for (var i = 0; i <= prices.size; i++) {
 if (price[i] > 20) {
 sum += price[i] * 0.9
 }}
 }} val prices = listOf(20, 12, 15, 21, 25, 28, 30)
32. var sum = 0.0 for (var i = 0; i < prices.size; i++) {
 if (price[i] > 20) {
 sum += price[i] * 0.9
 }}
 }} Example val prices = listOf(20, 12, 15, 21, 25, 28, 30)
33. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example var sum = 0.0 for (price in prices) {
 if (price > 20) {
 sum += price * 0.9
 }}
 }}
34. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum() var sum = 0.0 for (price in prices) {
 if (price > 20) {
 sum += price * 0.9
 }}
 }}
35. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
36. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
37. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
38. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
39. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
40. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum() Important: 1. No import = stdlib 2. Cross-platform
41. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
42. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum() // Returns list containing only elements matching [predicate] fun <T> filter(predicate: (T) -> Boolean): List<T>
43. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum() // Returns list containing only elements matching [predicate] fun <T> filter(predicate: (T) -> Boolean): List<T>
44. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example // Returns list containing elements transformed by [transform] fun <T, R> map(transform: (T) -> R): List<R> val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
45. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example // Returns list containing elements transformed by [transform] fun <T, R> map(transform: (T) -> R): List<R> val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
46. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum() Higher level, more readable & closer to the Business Intent
47. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum() var sum = 0.0 for (price in prices) {
 if (price > 20) {
 sum += price * 0.9
 }}
 }}
48. Another Example
49. You’re a Blog admin: “Calculate average blogpost length of all your blog’s Users that speak Polish” Example
50. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example
51. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val users = db.getAllUsers()
52. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = ??? val users = db.getAllUsers()
53. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users val users = db.getAllUsers()
54. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { ??? }} val users = db.getAllUsers()
55. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }} val users = db.getAllUsers()
56. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }
 .map { ??? }} val users = db.getAllUsers()
57. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }
 .map { user -> user.posts }} val users = db.getAllUsers()
58. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }
 .map { user -> user.posts } // Return type is: List<List<Post>> // But we need: List<Post> val users = db.getAllUsers()
59. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }
 .map { user -> user.posts } val users = db.getAllUsers()
60. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }
 .flatMap { user -> user.posts } val users = db.getAllUsers()
61. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }
 .flatMap { user -> user.posts } // Returns a single list with all elements yielded from // [transform] invoked on on each element of original collection. fun <T, R> flatMap(transform: (T) -> Iterable<R>): List<R> val users = db.getAllUsers()
62. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }
 .flatMap { user -> user.posts } // Returns a single list with all elements yielded from // [transform] invoked on on each element of original collection. fun <T, R> flatMap(transform: (T) -> Iterable<R>): List<R> val users = db.getAllUsers()
63. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }
 .flatMap { user -> user.posts } // Returns a single list with all elements yielded from // [transform] invoked on on each element of original collection. fun <T, R> flatMap(transform: (T) -> Iterable<R>): List<R> val users = db.getAllUsers()
64. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }
 .flatMap { user -> user.posts } val users = db.getAllUsers()
65. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }
 .flatMap { user -> user.posts }
 .map { ??? }} val users = db.getAllUsers()
66. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }} val users = db.getAllUsers()
67. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .filter { user -> user.language == "PL" }
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }
 .average() val users = db.getAllUsers()
68. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .take(100)
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }
 .average() val users = db.getAllUsers()
69. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .take(100)
 .flatMap { user -> user.posts } .map { post -> post.body.length } .count() val users = db.getAllUsers()
70. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .take(100)
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }
 .reduce { acc, length -> acc + length } val users = db.getAllUsers()
71. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .take(100)
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }
 .reduce { acc, length -> acc + length }} val users = db.getAllUsers() // Returns a single value computed by accumulating values // returned from applying [operation] to each element. fun <S, T:S> reduce(operation: (acc: S, T) -> S): S
72. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val avgPolishPostLength = users
 .take(100)
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }
 .fold(0) { acc, _ -> acc + 1 }} val users = db.getAllUsers() // Accumulates value starting with [initial] and applying // [operation] to current accumulator value and each element. fun <T, R> fold(initial: R, operation: (acc: R, T) -> R): R
73. Benefits
74. • No explicit mutation, reassignment, iteration etc. = less error prone • Low-level details controlled by the library = may be optimized under the hood • More expressive, more readable • Easy to enhance & modify the logic • Closer to the business intent Benefits
75. Functional -vs- Object-Oriented
76. Functional -vs- Object-Oriented
77. Functional + Object-Oriented
78. // Returns list containing only elements matching [predicate] fun <T> filter(predicate: (T) -> Boolean): List<T> // Returns list containing elements transformed by [transform] fun <T, R> map(transform: (T) -> R): List<R> // Flattens nested lists into single list fun <T, R> flatMap(transform: (T) -> Iterable<R>): List<R> // Accumulates value by applying [operation] fun <S, T:S> reduce(operation: (acc: S, T) -> S): S // Accumulates value, starting with [initial] fun <T, R> fold(initial: R, operation: (acc: R, T) -> R): R Common Specialized Functions
80. Functional
81. Functional + Reactive
82. Reactive
83. What is Reactive Programming?
84. Reactive Programming Programming with
 Asynchronous Event Streams
85. Reactive Programming Programming with
 Asynchronous Event Streams
86. Observer Pattern on Steroids Reactive Programming
87. Observer Pattern on Functional Steroids Reactive Programming
88. Reactive Programming Superpowered Data
89. 1 5 12 3 7 4
90. 1 filter(x > 4) 5 12 3 7 4
91. 1 filter(x > 4) 5 12 7 5 12 3 7 4
92. 1 filter(x > 4) 5 12 7 map(x + 2) 5 12 3 7 4
93. 1 filter(x > 4) 5 12 7 map(x + 2) 7 14 9 5 12 3 7 4
94. 1 filter(x > 4) 5 12 7 map(x + 2) 7 14 9 5 12 3 7 4
95. 1 filter(x > 4) 5 12 7 map(x + 2) 7 14 9 5 12 3 7 4
96. 1 filter(x > 4) 5 12 7 map(x + 2) 7 14 9 5 12 3 7 4
97. 1 filter(x > 4) 5 12 7 map(x + 2) 7 14 9 5 12 3 7 4
98. 1 filter(x > 4) 5 12 7 map(x + 2) 7 14 9 5 12 3 7 4
99. 5 12 7 map(x + 2) Stream Events Operator
100. 5 12 7 map(x + 2) Stream Events Infinite Operator
101. 5 12 7 map(x + 2) Stream Events Error Operator
102. 5 12 7 map(x + 2) Stream Events Complete Operator
103. Implementation
104. Reactive Extensions Implementation
105. Rx Implementation
106. • RxJava • RxJS • Rx.NET • RxScala • RxClosure • RxCpp Implementation • RxPython • RxGo • RxKotlin • RxSwift • RxPHP • RxDart
107. Stream
108. Stream Observable<T>
109. Stream Observable<T> List<T> -vs-
110. Creating a Stream
111. Observable.just(1) Observable.just(true) Observable.just(user) Observable.just("one", "two", "three") Creating a Stream Observable.fromIterable(users) Observable.fromArray(usersArray) Observable.fromCallable(this::sendRequest) Observable.fromFuture(future) Observable.defer(...) Observable.create(...)
112. Observable.just(1)) Creating a Stream .subscribe { item ->
 print("Item = $item")
 }} // Item = 1
113. Observable.just(true)) .subscribe { item ->
 print("Item = $item")
 }} // Item = true Creating a Stream
114. Observable.just(user)) .subscribe { item ->
 print("Item = $item")
 }} // Item = User(language="PL",posts=...) Creating a Stream
115. Observable.just("one", "two", "three") .subscribe { item ->
 print("Item = $item")
 }} // Item = one // Item = two // Item = three Creating a Stream
116. Observable.just(user1, user2, ...)) .subscribe { item ->
 print("Item = $item")
 }} // Item = User(language="PL",posts=...) // Item = User(language="EN",posts=...) // ... Creating a Stream
117. Observable.fromIterable(users)) .subscribe { item ->
 print("Item = $item")
 }} // Item = User(language="PL",posts=...) // Item = User(language="EN",posts=...) // Item = User(language="PL",posts=...) // Item = User(language="PL",posts=...) ... Creating a Stream
118. Observable.fromIterable(users)) .subscribe { item ->
 print("Item = $item")
 }} // Item = User(language="PL",posts=...) // Item = User(language="EN",posts=...) // Item = User(language="PL",posts=...) // Item = User(language="PL",posts=...) ... Creating a Stream Where are my Steroids?
119. API
120. API abstract class Observable<T> { }} interface Observer<T> {
 }}
121. API abstract class Observable<T> { fun <T> filter(predicate: (T) -> Boolean): Observable<T> fun <T, R> map(transform: (T) -> R): Observable<R> // // ...13k lines of code... // }} interface Observer<T> {
 }}
122. API abstract class Observable<T> { fun <T> filter(predicate: (T) -> Boolean): Observable<T> fun <T, R> map(transform: (T) -> R): Observable<R> // // ...13k lines of code... // }} interface Observer<T> {
 fun onNext(@NonNull t: T)
 fun onError(@NonNull e: Throwable)
 fun onComplete()
 }}
123. Observable.just("5", "8", "3", "7") .subscribe { item ->
 print("Item = $item")
 }} Transforming a Stream
124. Observable.just("5", "8", "3", "7") .map(String::toInt) .subscribe { item ->
 print("Item = $item")
 }} Transforming a Stream
125. Observable.just("5", "8", "3", "7") .map(String::toInt) .filter { item -> item > 5 } .subscribe { item ->
 print("Item = $item")
 }} // Item = 8 // Item = 7 Transforming a Stream
126. Introducing Time
127. Observable.interval(1, TimeUnit.SECONDS) Interval .subscribe { item ->
 print("Item = $item")
 }} //00:00: Item = 0 //00:01: Item = 1 //00:02: Item = 2 //00:03: Item = 3 //00:04: Item = 4 //...
128. Observable.interval(1, TimeUnit.SECONDS) Interval .map { item -> item * item } .subscribe { item ->
 print("Item = $item")
 }}
129. Observable.interval(1, TimeUnit.SECONDS) Interval .map { item -> item * item }. .take(3) .subscribe { item ->
 print("Item = $item")
 }} //00:00: Item = 0 //00:01: Item = 1 //00:02: Item = 4
130. // RxBinding RxView.clicks(button) // Observable<Object> .map { click -> 1 } .scan { acc, next -> acc + next } UI Events .subscribe { count ->
 print("Count = $count")
 } // Count = 1 // Count = 2 // Count = 3 // Count = 4 // ...
131. // Retrofit myService.getUsers() // Observable<User> .map { user -> user.posts.size } .reduce { acc, next -> acc + next } Network Requests .subscribe { count ->
 print("Post count = $count")
 } // Post count = 120
132. // Task: perform network request after each click Combining // Return type: Observable<Observable<User>> // But we want: Observable<User> val buttonClicks = RxView.clicks(button) val userInfoRequest = myService.getUserInfo() buttonClicks .map { click -> myService.getUserInfo() }
133. // Returns Observable that emits all items emitted by // Observables returned by [mapper] fun <T, R> flatMap(mapper: (T) -> Observable<R>): Observable<R> buttonClicks .flatMap { click -> myService.getUserInfo() } Combining val buttonClicks = RxView.clicks(button) val userInfoRequest = myService.getUserInfo() // Task: perform network request after each click
134. Combining .map { user -> user.firstName } .subscribe { firstName ->
 print("firstName = $firstName")
 } // firstName = John val buttonClicks = RxView.clicks(button) val userInfoRequest = myService.getUserInfo() buttonClicks .flatMap { click -> myService.getUserInfo() } // Task: perform network request after each click
135. // Task: do the same thing on btn1 & btn2 click Combining val btn1Clicks = RxView.clicks(button1) val btn2Clicks = RxView.clicks(button2) btn1Clicks .map { click -> "Click!" } .subscribe { msg ->
 print("msg = $msg")
 }}
136. // Task: do the same thing on btn1 & btn2 click Combining val btn1Clicks = RxView.clicks(button1) val btn2Clicks = RxView.clicks(button2) Observable.merge(btn1Clicks, btn2Clicks) .map { click -> "Click!" } .subscribe { msg ->
 print("msg = $msg")
 }} // Merges two (or more) Observables into a single one. fun <T> merge(s1: Observable<T>, s2: Observable<T>): Observable<T>
137. fun fetchUser(): User { /* fetch from network */ } Threading Observable.fromCallable(this::fetchUser) .subscribeOn(Schedulers.io()) .subscribe { user ->
 print("User = $user")
 }}
138. fun fetchUser(): User { /* fetch from network */ } Threading Observable.fromCallable(this::fetchUser) .subscribeOn(Schedulers.io()) .subscribe { user -> statusLabel.text = user.firstName
 }}
139. fun fetchUser(): User { /* fetch from network */ } Threading .subscribe { user -> statusLabel.text = user.firstName
 }} Observable.fromCallable(this::fetchUser) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread())
140. Netflix
141. Tips
142. Tips • Start small - get used to FP first
 (be declarative, avoid side-effects etc.) • RX is not an architecture. It's a Tool.
 So use it wisely • Subtask = flatMap • Remember that error = end of Stream
143. Use RX when you need... • Composing & orchestrating multiple async events • Manipulating time (delay, timeout etc.) • Cancellation of async events
144. Conclusions
145. • Great for composing/orchestrating multiple Event streams • 100+ operators for creating, transforming & combining streams • Declarative threading • Cancellation of async tasks • Do not overuse for simple tasks Conclusions on RX
146. How to Start?
147. How to Start? • ReactiveX.io • github.com/ReactiveX • rxmarbles.com • geekydevs.com/rx
148. Thank You
149. Thank You Any questions?