Introduction to Functional-Reactive Programming v2

v2.0

Transcript

1. Grzegorz Dyrda Geeky Devs Studio Introduction to Functional-Reactive Programming
2. Functional-Reactive Programming
3. Functional-Reactive Programming Why?
4. Why? • Java 9 + Reactive Streams (JEP 266) • Spring WebFlux, Eclipse Vert.x • Angular, Cycle.js, React (Native) • Android Architecture Components, Room, Retrofit… Airbnb MvRx
5. Functional-Reactive
6. Functional + Reactive
7. Functional Part 1:
8. You cannot understand Functional-Reactive programming, if you don’t understand Functional programming.
9. What is Functional Programming?
10. 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.
11. Functional Programming …is about moving from
 the imperative
 to declarative style.
12. The world’s most popular functional language is… Excel
13. =IF(A6="", IF(C5<>"", C5, IFERROR(MATCH("?*", A6:$A$20, 0)-1, ROWS(A6:$A$20))&" in "&VLOOKUP(A5,$H$6:$I$8, 2, 0)), "") Excel =IF(MONTH($C$3)<>MONTH($C$3-(WEEKDAY($C$3;1)-($A$1-1))- IF((WEEKDAY($C$3;1)-($A$1-1))<=0;7;0)+(ROW(F7)-J3- ROW($D$6))*7+(COLUMN(F7)-COLUMN($D$6)+1));"";$C$3- (WEEKDAY($C$3;1)-($A$1-1))-IF((WEEKDAY($C$3;1)- ($A$1-1))<=0;7;0)+(ROW(F7)-J3-ROW($D$6))*7+(COLUMN(F7)- COLUMN($D$6)+1))
14. Language Support
15. • Functions as first-class citizens • Higher-order functions • Lambda expressions • Immutable data types • Functions are closures Language Support JAVA 8+ APPROVED
16. Example
17. Client says: “Make a sum of all our prices
 that are higher than $20,
 discounted by 10%” Example
18. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example
19. 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)
20. 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)
21. 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
 }}
 }}
22. 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
 }}
 }}
23. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
24. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
25. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
26. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
27. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
28. 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
29. val prices = listOf(20, 12, 15, 21, 25, 28, 30) Example val sum = prices
 .filter { price -> price > 20 }
 .map { price -> price * 0.9 }
 .sum()
30. 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>
31. 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>
32. 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()
33. 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()
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() Single, consistent, higher-level API. More readable & closer to the Business Intent
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() var sum = 0.0 for (price in prices) {
 if (price > 20) {
 sum += price * 0.9
 }}
 }}
36. Another Example
37. You’re a Blog admin: “Calculate average blogpost length of all your blog’s Users that speak Polish” Example
38. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example
39. data class Post(val title: String, val body: String)
 data class User(val language: String, val posts: List<Post>) Example val users = db.getAllUsers()
40. 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()
41. 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()
42. 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()
43. 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()
44. 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()
45. 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()
46. 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()
47. 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()
48. 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()
49. 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()
50. 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()
51. 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()
52. 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()
53. 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()
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 { user -> user.language == "PL" }
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }} 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" }
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }
 .average() 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" }
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }
 .average() val users = db.getAllUsers() // Easy to maintain and modify
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" }
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }
 .average() 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
 .take(100)
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }
 .average() 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
 .take(100)
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }
 .average() 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
 .take(100)
 .flatMap { user -> user.posts } .map { post -> post.body.length } .count() 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
 .take(100)
 .flatMap { user -> user.posts }
 .map { post -> post.body.length }
 .reduce { acc, length -> acc + length } 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
 .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
63. 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
64. 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
65. Benefits
66. • 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
67. Functional -vs- Object-Oriented
68. Functional -vs- Object-Oriented
69. Functional + Object-Oriented
70. // 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
73. Functional…
74. Functional + Reactive
75. Reactive Part 2:
76. What does is mean to be “Reactive”?
77. var a = 1 var b = 2 var c = a + b print("c = $c") What does is mean to be “Reactive”? // ???
78. var a = 1 var b = 2 var c = a + b print("c = $c") What does is mean to be “Reactive”? // c = 3
79. var a = 1 var b = 2 var c = a + b a = 2 print("c = $c") What does is mean to be “Reactive”? // ???
80. var a = 1 var b = 2 var c = a + b a = 2 print("c = $c") What does is mean to be “Reactive”? // c = 3
81. The world’s most popular reactive system is… Excel
82. Excel
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. 1 5 12 3 7 4 This can be anything: Number, Object, Blog Post etc.
89. 1 filter(x > 4) 5 12 3 7 4
90. 1 filter(x > 4) 5 12 7 5 12 3 7 4
91. 1 filter(x > 4) 5 12 7 map(x + 2) 5 12 3 7 4
92. 1 filter(x > 4) 5 12 7 map(x + 2) 7 14 9 5 12 3 7 4
93. 1 filter(x > 4) 5 12 7 map(x + 2) 7 14 9 5 12 3 7 4 So far everything was…
 Synchronous
94. 1 filter(x > 4) 5 12 7 map(x + 2) 7 14 9 5 12 3 7 4 Introducing…
 Time
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. 1 filter(x > 4) 5 12 7 map(x + 2) 7 14 9 5 12 3 7 4
100. 1 filter(x > 4) 5 12 7 map(x + 2) 7 14 9 5 12 3 7 4
101. 5 12 7 map(x + 2) (Asynchronous Event) Stream Events Operator
102. 5 12 7 map(x + 2) Stream Events Infinite Operator
103. 5 12 7 map(x + 2) Stream Events Error Operator
104. 5 12 7 map(x + 2) Stream Events Complete Operator
105. Implementation
106. Akka Reactor Reactive Extensions Vert.x xstream Implementation
107. Akka Reactor Reactive Extensions Vert.x xstream Implementation
108. Rx Implementation
109. • RxJava • RxJS • Rx.NET • RxScala • RxClojure • RxCpp Implementation • RxPython • RxGo • RxKotlin • RxSwift • RxPHP • RxDart
110. Stream
111. Stream Observable<T>
112. Stream Observable<T> List<T> -vs-
113. Creating a Stream
114. 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(...)
115. Observing a Stream
116. Observable.just(1)) Observing a Stream .subscribe { item ->
 print("Item = $item")
 }} // Item = 1
117. Observing a Stream // Subscribes the given Observer to this Observable instance. fun <T> subscribe(observer: Observer<T>): Unit interface Observer<T> {
 fun onNext(t: T)
 fun onError(e: Throwable)
 fun onComplete() ...
 }} // Subscribes to an ObservableSource and provides callbacks. fun <T> subscribe(onNext: (T) -> Unit, onError: (Throwable) -> Unit, onComplete: () -> Unit): Unit
118. Observable.just(1)) Observing a Stream .subscribe { item ->
 print("Item = $item")
 }} // Item = 1
119. Observable.just(true)) .subscribe { item ->
 print("Item = $item")
 }} // Item = true Observing a Stream
120. Observable.just(user)) .subscribe { item ->
 print("Item = $item")
 }} // Item = User(language="PL",posts=...) Observing a Stream
121. Observable.just("one", "two", "three") .subscribe { item ->
 print("Item = $item")
 }} // Item = one // Item = two // Item = three Observing a Stream
122. 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=...) ... Observing a Stream
123. 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=...) ... Where are my Steroids? Observing a Stream
124. Transforming a Stream
125. Observable.just("5", "8", "3", "7") .subscribe { item ->
 print("Item = $item")
 }} Transforming a Stream
126. Observable.just("5", "8", "3", "7") .map(String::toInt) .subscribe { item ->
 print("Item = $item")
 }} Transforming a Stream
127. 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
129. “There’s an App for that” Apple, 2009
130. “There’s an Operator for that” Reactive Extensions, 2018
131. ReactiveX Operators Creating: • create • defer • empty • error • fromArray • fromCallable • fromFuture • interval • just • … Transform/Filter: • buffer • flatMap • groupBy • map • scan • window • debounce • distinct • filter • … Combining: • combineLatest • withLatestFrom • merge • switch • zip Threading: • subscribeOn • observeOn • …
132. Introducing Time
133. 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 //...
134. Observable.interval(1, TimeUnit.SECONDS) Interval .map { item -> item * item } .subscribe { item ->
 print("Item = $item")
 }}
135. 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
136. // RxBinding RxView.clicks(button) // Observable<Object> .map { click -> 1 } .scan { acc, next -> acc + next } UI Events // Similar to reduce(), but accumulates values over time, // each time passing the result of [operation] downstream. fun <T> scan(operation: (acc: T, T) -> T): Observable<T>
137. // 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 // ...
138. // 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
139. Threading
140. fun fetchUser(): User { /* fetch from network */ } Threading Observable.fromCallable(this::fetchUser) .subscribe { user ->
 print("User = $user")
 }} // Error: Network on the Main Thread!
141. fun fetchUser(): User { /* fetch from network */ } Threading Observable.fromCallable(this::fetchUser) .subscribe { user ->
 print("User = $user")
 }} .subscribeOn(Schedulers.io())
142. fun fetchUser(): User { /* fetch from network */ } Threading Observable.fromCallable(this::fetchUser) .subscribe { user ->
 print("User = $user")
 }} .subscribeOn(Schedulers.io())
143. fun fetchUser(): User { /* fetch from network */ } Threading Observable.fromCallable(this::fetchUser) .subscribe { user ->
 print("User = $user")
 }} .subscribeOn(Schedulers.io())
144. fun fetchUser(): User { /* fetch from network */ } Threading Observable.fromCallable(this::fetchUser) .subscribeOn(Schedulers.io()) .subscribe { user -> statusLabel.text = user.firstName
 }} // Error: Accessing UI from the background thread!
145. fun fetchUser(): User { /* fetch from network */ } Threading .subscribe { user -> statusLabel.text = user.firstName
 }} Observable.fromCallable(this::fetchUser) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread())
146. fun fetchUser(): User { /* fetch from network */ } Threading .subscribe { user -> statusLabel.text = user.firstName
 }} Observable.fromCallable(this::fetchUser) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread())
147. fun fetchUser(): User { /* fetch from network */ } Threading .subscribe { user -> statusLabel.text = user.firstName
 }} Observable.fromCallable(this::fetchUser) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) // OK
148. Combining Streams
149. // Task: perform network request after each click Combining Streams // Return type: Observable<Observable<User>> // But we want: Observable<User> val buttonClicks = RxView.clicks(button) val userInfoRequest = myService.getUserInfo() buttonClicks .map { click -> myService.getUserInfo() }
150. // 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() } val buttonClicks = RxView.clicks(button) val userInfoRequest = myService.getUserInfo() // Task: perform network request after each click Combining Streams
151. .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 Combining Streams
152. // Task: do the same thing on btn1 & btn2 click val btn1Clicks = RxView.clicks(button1) val btn2Clicks = RxView.clicks(button2) btn1Clicks .map { click -> "Click!" } .subscribe { msg ->
 print("msg = $msg")
 }} Combining Streams
153. // Task: do the same thing on btn1 & btn2 click 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> Combining Streams
154. Combining Streams
155. Combining Streams
156. Netflix
157. Netflix
158. Netflix
159. Netflix
160. Netflix
161. Netflix
162. Netflix
163. Netflix
164. Conclusions
165. • FRP is great for composing/ orchestrating multiple Event streams • “There’s an Operator for that” • Declarative Threading, Error handling, Cancellation of async tasks etc. • Do not overuse for simple tasks Conclusions
166. How to Start?
167. How to Start? • ReactiveX.io • github.com/ReactiveX • rxmarbles.com • geekydevs.com/rx
168. Thank You
169. Thank You Any questions?