The document outlines the agenda for a Scala workshop held in October 2017, detailing two days of topics including Scala basics, functional programming, collections, and best practices. It provides instructions on using Scala, its syntax for expressions and functions, data types, and collections, along with examples. Additional resources for learning Scala and testing with ScalaTest are also included.

1. SCALAWORKSHOPKRAKOW
OCTOBER2017-DAY1
Fredrik Vraalsen - Data Platform
1

2. TOPICS
• Language features
• Functional programming
• Best practices
2

3. AGENDADAY1-THEBASICS
• Intro
• Scala basics
• Expressions, methods and functions
• Collections I
3

4. AGENDADAY2-FP
• Classes and Pattern Matching
• Collections II
• Laziness, implicits, DSLs
• QA & Wrapup
4

5. SCALARESOURCES
• API docs: https://www.scala-lang.org/api/current/
• Guides and overviews: http://docs.scala-lang.org/overviews/
• Tutorials: http://docs.scala-lang.org/tutorials/
5

6. TWITTER-EFFECTIVESCALA
• Best practices
• (Formatting)
• Usage of language features
• http://twitter.github.io/effectivescala/
6

7. BEFOREWESTART
7
git clone https://github.schibsted.io/fredrik-vraalsen/scala-workshop.git

8. SCALA
• Hybrid FP + OO language
• Developed at EPFL by Martin Odersky
• First public release in 2004, 2.0 in 2006
8

9. SCALA
9
https://dzone.com/articles/scala-liftoff

10. SCALA
• Current release 2.12 in 2016
• Focus on Java 8 interop
• Scala 3.0 in the works (codename Dotty)
10

11. SCALABASICS

12. HELLOWORLD
~ $ cat > helloworld.scala
println("Hello world!")
^D
~ $
12

13. HELLOWORLD
~ $ cat > helloworld.scala
println("Hello world!")
^D
~ $ scala helloworld.scala
Hello world!
~ $
13

14. LITERALS
"Fredrik" // String
'c' // Char
true / false // Boolean
42 // Int
2147483648L // Long
3.1415927f // Float
3.141592653589793 // Double
Byte (8 bit)
Short (16 bit)
14

15. VALUES
val name: String = "Fredrik"
val age: Int = 41
15

16. TYPEINFERENCE
val name = "Fredrik" // String
val age = 41 // Int
16

17. VARIABLES
val name = "Fredrik" // String
val age = 41 // Int
age = 42 // Compile error!
17

18. VARIABLES
val name = "Fredrik" // String
var age = 41 // Int
age = 42 // Yay!!?
18

19. STRINGS
val greeting = "Hello " + name + "!"
val greeting = s"Hello $name!"
val greeting = "Have some more %.5f!".format(Math.PI)
val greeting = s"""Hello "$name!"
This is a
multiline greeting!"""
19

20. STRINGS
val greeting = "Hello " + name + "!"
val greeting = s"Hello $name!"
val greeting = "Have some more %.5f!".format(Math.PI)
val greeting = s"""|Hello "$name!"
|This is a
|multiline greeting!""".stripMargin
20

21. CASECLASSES
case class Person(name: String, age: Int)
val p = Person("Fredrik", 41)
p.name // "Fredrik"
p.age // 41
21

22. EQUALITY
val p1 = Person("Fredrik", 41)
val p2 = Person("Fredrik", 41)
p1 == p2 // true
p1 eq p2 // false
p1.name == p2.name // true
p1.name eq p2.name // true
p1.age == p2.age // true
p1.age eq p2.age // error: value eq is not a member of Int
22

23. REPL
~ $ scala
Welcome to Scala 2.12.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_152).
Type in expressions for evaluation. Or try :help.
scala>
23

24. REPL
~ $ scala
Welcome to Scala 2.12.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_152).
Type in expressions for evaluation. Or try :help.
scala> case class Person(name: String, age: Int)
defined class Person
scala>
24

25. REPL
~ $ scala
Welcome to Scala 2.12.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_152).
Type in expressions for evaluation. Or try :help.
scala> case class Person(name: String, age: Int)
defined class Person
scala> val p = Person("Fredrik", 41)
p: Person = Person(Fredrik,41)
scala>
25

26. REPL
~ $ scala
Welcome to Scala 2.12.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_152).
Type in expressions for evaluation. Or try :help.
scala> case class Person(name: String, age: Int)
defined class Person
scala> val p = Person("Fredrik", 41)
p: Person = Person(Fredrik,41)
scala> p.name
res0: String = Fredrik
scala>
26

27. SCALATEST
• Multiple testing styles (xUnit, BDD, etc.)
• Asserts or matchers
27

28. SCALATEST
28

29. SCALATEST
29

30. SCALATEST
result should be (3)
result shouldBe 3
result should equal (3)
result shouldEqual(3)
result should === (3)
result should not be 3
result should !== (3)
result should be < 7
result should have length 3 // or size
result should startWith (“Hello”) // or endWith / contain
30

31. SCALATEST
• Run tests
• With Gradle: ./gradlew test -t
• In IDE: Ctrl+Shift+F10 or Ctrl+Shift+R
• More info at http://scalatest.org/
31

32. EXERCISE1
32

33. EXPRESSIONS,METHODSAND
FUNCTIONS

34. EXPRESSIONS
• Every expression returns a value
34

35. EXPRESSIONS
var sign: String = _ // null
if (i >= 0) {
sign = "Positive"
} else {
sign = "Negative"
}
35

36. EXPRESSIONS
val sign: String = if (i >= 0) {
"Positive"
} else {
"Negative"
}
36

37. EXPRESSIONS
val sign = if (i >= 0) {
"Positive"
} else {
"Negative"
}
37

38. EXPRESSIONS
val sign = if (i >= 0) "Positive" else "Negative"
38

39. EXPRESSIONS
val sign = if (i >= 0) "Positive" else “Negative"
String sign = i >= 0 ? "Positive" : “Negative" // Java
39

40. EXPRESSIONS
val evenNumbers = collection.mutable.ArrayBuffer[Int]()
for (i <- 1 to 10) evenNumbers.append(i * 2)
40

41. EXPRESSIONS
val evenNumbers = for (i <- 1 to 10) yield i * 2
val res = try callMethod() catch { case ex => defaultValue }
val avg = {
val sum = numbers.sum
sum / numbers.size
}
41

42. METHODS
42

43. METHODS
def add(a: Int, b: Int): Int = {
return a + b;
}
43
Keyword
Name Parameters Returntype
Body

44. METHODS
def add(a: Int, b: Int): Int = {
return a + b
}
44
Keyword
Name Parameters Returntype
Body

45. METHODS
def add(a: Int, b: Int): Int = {
a + b
}
45
Keyword
Name Parameters Returntype
Body

46. METHODS
def add(a: Int, b: Int): Int = a + b
46
Keyword
Name Parameters Returntype
Body

47. METHODS
def add(a: Int, b: Int) = a + b
47
Keyword
Name Parameters Returntype
Body

48. METHODS
def add(a: Int, b: Int) = a + b
48

49. METHODS
def add(a: Int, b: Int) = a + b
add(2, 2) // 4
49

50. NAMEDANDDEFAULTARGUMENTS
def resize(width: Int, height: Int, notify: Boolean = true)
50

51. NAMEDANDDEFAULTARGUMENTS
def resize(width: Int, height: Int, notify: Boolean = true)
resize(100, 200)
51

52. NAMEDANDDEFAULTARGUMENTS
def resize(width: Int, height: Int, notify: Boolean = true)
resize(100, 200)
resize(100, 200, false)
52

53. NAMEDANDDEFAULTARGUMENTS
def resize(width: Int, height: Int, notify: Boolean = true)
resize(100, 200)
resize(100, 200, false)
resize(100, 200, notify = false)
53

54. NAMEDANDDEFAULTARGUMENTS
def resize(width: Int, height: Int, notify: Boolean = true)
resize(100, 200)
resize(100, 200, false)
resize(100, 200, notify = false)
resize(width = 100, height = 200)
resize(height = 200, width = 100)
resize(height = 200, width = 100, notify = false)
54

55. FUNCTIONS
55

56. FUNCTIONS
• Functions are first class citizens
• Create, assign, apply
56

57. METHODS
def add(a: Int, b: Int) = a + b
57

58. FUNCTIONS
(a: Int, b: Int) => a + b
58

59. FUNCTIONS
val add = (a: Int, b: Int) => a + b
59

60. FUNCTIONS
val add = (a: Int, b: Int) => a + b // (Int, Int) => Int
60

61. FUNCTIONS
val add = new Function2[Int, Int, Int] {
def apply(a: Int, b: Int): Int = a + b
}
61

62. FUNCTIONS
val add = (a: Int, b: Int) => a + b
add.apply(2, 2) // 4
62

63. FUNCTIONS
val add = (a: Int, b: Int) => a + b
add(2, 2) // 4
63

64. PARTIALFUNCTIONS
64

65. PARTIALFUNCTIONS
val isEven: PartialFunction[Int, String] = {
case x if x % 2 == 0 => x + " is even"
}
isEven(2) // "2 is even"
isEven(3) // throws MatchError
65

66. PARTIALFUNCTIONS
val isEven: PartialFunction[Int, String] = {
case x if x % 2 == 0 => x + " is even"
}
isEven.isDefinedAt(2) // true
isEven.isDefinedAt(3) // false
66

67. EXERCISE2
67

68. COLLECTIONSI

69. COLLECTIONS
val numbers = List(17, 42, 314)
69

70. COLLECTIONS
val numbers = List(17, 42, 314)
numbers(1) // 42
70

71. COLLECTIONS
val numbers = List(17, 42, 314)
numbers(1) // 42
val clicks = Map("vg" -> 231232, "aftenposten" -> 158742)
71

72. COLLECTIONS
val numbers = List(17, 42, 314)
numbers(1) // 42
val clicks = Map("vg" -> 231232, "aftenposten" -> 158742)
clicks("vg") // 231232
72

73. COLLECTIONS
val numbers = List.apply(17, 42, 314)
numbers.apply(1) // 42
val clicks = Map.apply("vg" -> 231232, "aftenposten" -> 158742)
clicks.apply("vg”) // 231232
73

74. COLLECTIONS
• Collections ≈ partial functions
74

75. COLLECTIONOPERATIONS
75

76. CONSTRUCTION
val numbers = List(42, 314)
val moreNumbers = 17 :: numbers // List(17, 42, 314)
val fromScratch = 1 :: 2 :: 3 :: Nil // List(1, 2, 3)
76

77. HEADSANDTAILS
val numbers = List(17, 42, 314)
val first = numbers.head // 17
val rest = numbers.tail // List(42, 314)
77

78. SIZE
val names: List[String] = ...
val numberOfNames = names.size
78

79. SIZE
val names: List[String] = ...
val numberOfNames = names.length
79

80. EMPTINESS
val names: List[String] = ...
val empty = names.length == 0
80

81. EMPTINESS
val names: List[String] = ...
val empty = names.isEmpty
81

82. EMPTINESS
val names: List[String] = ...
val notEmpty = !names.isEmpty
82

83. EMPTINESS
val names: List[String] = ...
val notEmpty = names.nonEmpty
83

84. FILTERING
val names: List[String] = ...
val skywalkers = names.filter( ??? )
84

85. FILTERING
val names: List[String] = ...
val skywalkers = names.filter( ??? )
85
(A) => Boolean

86. FILTERING
val names: List[String] = ...
val skywalkers = names.filter( ??? )
86
(String) => Boolean

87. FILTERING
val names: List[String] = ...
val skywalkers = names.filter((name: String) => name.contains("Skywalker"))
87

88. FILTERING
val names: List[String] = ...
val skywalkers = names.filter(name => name.contains("Skywalker"))
88

89. FILTERING
val names: List[String] = ...
val skywalkers = names.filter(_.contains(“Skywalker"))
89

90. FILTERING
val names: List[String] = ...
val nameFilter: (String) => Boolean = _.contains(“Skywalker")
val skywalkers = names.filter(nameFilter)
90

91. FILTERING
val names: List[String] = ...
val nameFilter = (name: String) => name.contains("Skywalker")
val skywalkers = names.filter(nameFilter)
91

92. FILTERING
val names: List[String] = ...
def nameFilter(name: String) = name.contains("Skywalker")
val skywalkers = names.filter(nameFilter)
92

93. ITERATING
val names: List[String] = ...
names.foreach(name => println(name))
93

94. ITERATING
val names: List[String] = ...
names.foreach(println(_))
94

95. ITERATING
val names: List[String] = ...
names.foreach(println)
95

96. TRANSFORMING
val people: List[Person] = ...
val names = people.map( ??? )
96
(A) => B

97. TRANSFORMING
val people: List[Person] = ...
val names = people.map( ??? )
97
(Person) => B

98. TRANSFORMING
val people: List[Person] = ...
val names = people.map(person => person.name)
98
(Person) => String

99. TRANSFORMING
val people: List[Person] = ...
val names = people.map(person => person.name) // List[String]
99
(Person) => String

100. TRANSFORMING
val people: List[Person] = ...
val names = people.map(_.name) // List[String]
100
(Person) => String

101. SORTING
val names: List[String] = ...
val sortedNames = names.sorted
101

102. SORTING
val names: List[String] = ...
val reverseNames = names.sorted.reverse
102

103. SORTING
val names: List[String] = ...
val reverseNames = names.sorted(Ordering[String].reverse)
103

104. SORTING
val people: List[Person] = ...
val sortedByName = people.???
104

105. SORTING
val people: List[Person] = ...
val sortedByName = people.sortBy( ??? )
105
(A) => B // Ordering[B]

106. SORTING
val people: List[Person] = ...
val sortedByName = people.sortBy( ??? )
106
(Person) => B // Ordering[B]

107. SORTING
val people: List[Person] = ...
val sortedByName = people.sortBy(person => person.name)
107
(Person) => String // Ordering[String]

108. SORTING
val people: List[Person] = ...
val sortedByName = people.sortBy(_.name)
108
(Person) => String // Ordering[String]

109. SORTING
val people: List[Person] = ...
val reverseByName = people.sortBy(_.name)(Ordering[String].reverse)
109

110. AGGREGATING
val numbers = List(17, 42, 314)
val max = numbers.max // 314
val sum = numbers.sum // 373
110

111. COLLECTIONTYPES
• Sequences, Sets and Maps
• Immutable vs Mutable
• Performance
111

112. SEQUENCES
Immutable
• List
• Vector
• Queue
• Range
112
Mutable
• LinkedList
• ArrayBuffer / ListBuffer
• Queue
• ArrayStack

113. PERFORMANCE
113
Head Tail Length Lookup Update Prepend Append Insert
List 1 1 n n n 1 n -
Vector 1 * 1 * 1 * ? 1 * 1 * 1 * 1 * -
Queue 1 ** 1 ** n n n 1 1 -
ArrayBuffer 1 n 1 1 1 n 1 ** n
* = effectively ** = amortized

114. SETSANDMAPS
• HashSet
• TreeSet
• LinkedHashSet
• BitSet
114
• HashMap
• TreeMap
• LinkedHashMap
• IntMap / LongMap

115. COLLECTIONSAPI
• isEmpty, nonEmpty, size
• indexOf, contains, exists, forall, count
• head, tail, headOption, tailOption
• take, drop, takeWhile, dropWhile
• map, flatMap, foreach
• filter, filterNot, collect, partition
• sum, product, min, max, aggregate, fold
• reverse, sorted, sortBy, groupBy
• splitAt, grouped, sliding, combinations
115

116. MOREREADING
• http://docs.scala-lang.org/overviews/collections/overview.html
116

117. EXERCISE3
117

118. SCALAWORKSHOPKRAKOW
OCTOBER2017-DAY2
Fredrik Vraalsen - Data Platform
118

119. AGENDADAY2-FP
• Classes and Pattern Matching
• Collections II
• Laziness, implicits, DSLs
• QA & Wrapup
119

120. CLASSESANDPATTERNMATCHING

121. CLASSES
• Classes
• Traits
• Tuples
• Option
• Pattern matching
121

122. CLASSES
class Person(val name: String, var age: Int)
122

123. CLASSES
class Person(val name: String, var age: Int) {
// properties
// methods
// initialisation
}
123

124. CLASSES
package com.schibsted.model
import some.package.{ClassA, ClassB}
import some.other.package._
class Person(val name: String, var age: Int) {
// properties
// methods
// initialisation
}
124

125. CLASSES
class Person(val name: String, var age: Int)
val me = new Person("Fredrik", 41)
me.name // "Fredrik"
me.age // 41
me.age = 42
125

126. SINGLETONOBJECTS
object Person {
val constant = 42
def encode(user: Person): Json = ...
def decode(json: Json): Person = ...
def find(userId: Long): Person = ...
}
126

127. CASECLASSES
• Auto-generated methods
• Companion Object
127

128. CASECLASSES
case class Person(name: String, age: Int)
128

129. CASECLASSES
case class Person(name: String, age: Int)
class Person(val name: String, val age: Int) {
def copy(name: String, age: Int): Person
override def toString(): String
// hashCode, equals, etc.
}
129

130. CASECLASSES
case class Person(name: String, age: Int)
class Person(val name: String, val age: Int) {
def copy(name: String, age: Int): Person
override def toString(): String
// hashCode, equals, etc.
}
object Person {
def apply(name: String, age: Int): Person
// more
}
130

131. CASECLASSES
case class Person(name: String, age: Int)
val me = Person("Fredrik", 41)
val olderMe = me.copy(age = 42)
131

132. CASECLASSES
case class Person(name: String, age: Int)
val me = Person("Fredrik", 41)
val olderMe = me.copy(age = 42)
class Person(val name: String, val age: Int) {
def copy(name: String = this.name, age: Int = this.age): Person
...
}
132

133. INHERITANCE
• Single inheritance
133

134. INHERITANCE
abstract class Shape(val color: String) {
def area: Double
}
class Circle(val radius: Double, color: String) extends Shape(color) {
def area = radius * radius * Math.PI
}
val c = new Circle(1.0, "blue")
c.color // "blue"
c.area // 3.14159...
134

135. TRAITS
• Let’s you mix code into your class
• “Interfaces on steroids”
• Methods, values (abstract or implemented)
135

136. TRAITS
trait Ordered[T] {
def compare(that: T): Int
}
136

137. TRAITS
trait Ordered[T] {
def compare(that: T): Int
def < (that: A): Boolean = (this compare that) < 0
def > (that: A): Boolean = (this compare that) > 0
def <= (that: A): Boolean = (this compare that) <= 0
def >= (that: A): Boolean = (this compare that) >= 0
}
137

138. TRAITS
case class Person(name: String, age: Int)
extends Ordered[Person] {
override def compare(that: Person) = this.age - that.age
}
138

139. TRAITS
case class Person(name: String, age: Int)
extends Ordered[Person] {
override def compare(that: Person) = this.age - that.age
}
val a = Person("Fredrik", 41)
val b = Person("Johannes", 8)
a.>(b) // true
139

140. TRAITS
case class Person(name: String, age: Int)
extends Ordered[Person] {
override def compare(that: Person) = this.age - that.age
}
val a = Person("Fredrik", 41)
val b = Person("Johannes", 8)
a > b // true
140

141. TRAITS
case class Person(name: String, age: Int)
extends Ordered[Person] {
override def compare(that: Person) = this.age compare that.age
}
val a = Person("Fredrik", 41)
val b = Person("Johannes", 8)
a > b // true
141

142. MULTIPLETRAITS
case class Person(name: String, age: Int)
extends Ordered[Person]
with Cloneable
with Serializable {
override def compare(that: Person) = this.age compare that.age
}
142

143. TUPLES
• Unnamed structs
• Individually typed elements
143

144. TUPLES
val t1 = Tuple2("Fredrik", 41) // (String, Int)
val t2 = ("Fredrik", 41) // (String, Int)
t2._1 // "Fredrik"
t2._2 // 41
144

145. ADTS
• Algebraic Data Types
145

146. ADTS
sealed trait Tree
case class Node(left: Tree, right: Tree) extends Tree
case class Leaf(value: Int) extends Tree
val tree = Node(Node(Leaf(1), Leaf(2)), Leaf(3))
146
1 2
3

147. ADTS
sealed trait Tree[T]
case class Node[T](left: Tree[T], right: Tree[T]) extends Tree[T]
case class Leaf[T](value: T) extends Tree[T]
val tree = Node(Node(Leaf('a'), Leaf('b')), Leaf('c'))
147
a b
c

148. ADTS
sealed trait Json
case class JObject(fields: Map[String, Json]) extends Json
case class JArray(arr: List[Json]) extends Json
case class JString(str: String) extends Json
case class JNumber(num: BigDecimal) extends Json
case class JBool(value: Boolean) extends Json
case object JNull extends Json
val json = JObject(Map(
"name" -> JString("Fredrik"),
"age" -> JNumber(41)
))
148

149. ADTS
sealed trait Json
case class JObject(fields: Map[String, Json]) extends Json
case class JArray(arr: List[Json]) extends Json
case class JString(str: String) extends Json
case class JNumber(num: BigDecimal) extends Json
case class JBool(value: Boolean) extends Json
case object JNull extends Json
object JObject {
def apply(fields: (String, Json)*) = new JObject(fields.toMap)
}
val json = JObject(
"name" -> JString("Fredrik"),
"age" -> JNumber(41)
)
149

150. OPTIONALS
• Can contain an optional value of some type
• Transformations etc. work on the "happy path"
• Avoid null errors
150

151. OPTIONALS
val employees: Map[Int, Person] = …
employees(314)
151

152. OPTIONALS
val employees: Map[Int, Person] = …
employees.get(314) // Option[Person]
152

153. OPTIONALS
val employees: Map[Int, Person] = …
employees.get(314)
.map(_.name) // Option[String]
153

154. OPTIONALS
val employees: Map[Int, Person] = …
employees.get(314)
.map(_.name)
.getOrElse("Not found") // String
154

155. PATTERNMATCHING
• Values
• Types
• Structures
155

156. MATCHINGVALUES
val value = …
val result = value match {
case 1 => "number"
case "two" => "string"
case false => "boolean"
case _ => "unknown"
}
156

157. MATCHINGTYPES
val json = …
def jsonStr(json: Json) = json match {
case s: JString => '"' + s.str + '"'
case n: JNumber => n.num.toString
case b: JBool => b.value.toString
case JNull => "null"
}
val s = jsonStr(json)
157

158. MATCHINGSTRUCTURES
val json = …
val jsonStr = json match {
case JString(str) => '"' + str + '"'
case JNumber(num) => num.toString
case JBool(value) => value.toString
case JNull => "null"
}
158

159. MATCHINGSTRUCTURES
val tuple = …
val second = tuple match {
case (a, b) => b
}
159

160. MATCHINGSTRUCTURES
val tuple = …
val second = tuple match {
case (_, b) => b
}
160

161. MATCHINGSTRUCTURES
val tuple = …
val second = tuple match {
case ("special", b) => s"special $b"
case (_, b) => b
}
161

162. MATCHINGSTRUCTURES
val optional = …
val value = optional match {
case Some(value) => value
case None => defaultValue
}
162

163. MATCHINGSTRUCTURES
val optional = …
val value = optional match {
case Some(value) => value
case None => defaultValue
}
// optional.getOrElse(defaultValue)
163

164. MATCHINGSTRUCTURES
val list = …
val first = list match {
case head :: tail => head
case Nil => "Not found"
}
164

165. MATCHINGSTRUCTURES
val list = …
val value = list match {
case List(_, b) => b
case List(a, _*) => a
case Nil => "Not found"
}
165

166. MATCHINGREGULAREXPRESSIONS
val email = "(.*)@(.*..*)".r
"fredrik@vraalsen.no" match {
case email(user, domain) => s"User: $user, domain: $domain"
case _ => "Invalid email"
}
166

167. EXERCISE4
167

168. COLLECTIONSII

169. SUBLISTS
val numbers: List[Int] = List(1, 2, 3, 4, 5)
val (before, after) = numbers.splitAt(3) // (List(1, 2, 3), List(4, 5))
169

170. PARTITIONING
val people: List[Person] = ...
val adults = people.filter(_.age >= 18)
val kids = people.filterNot(_.age >= 18)
170

171. PARTITIONING
val people: List[Person] = ...
val (adults, kids) = people.partition(_.age >= 18)
171

172. SUBLISTS
val numbers: List[Int] = List(1, 2, 3, 4, 5)
val grouped = numbers.grouped(2) // List(1, 2), List(3, 4), List(5)
172

173. SUBLISTS
val numbers: List[Int] = List(1, 2, 3, 4, 5)
val grouped = numbers.sliding(3)
// List(1, 2, 3), List(2, 3, 4), List(3, 4, 5)
173

174. COMBINING
val numbers: List[Int] = List(17, 42)
val chars: List[Char] = List('a', 'b')
val combined = numbers.zip(chars) // List((17, 'a'), (42, 'b'))
174

175. COMBINING
val chars: List[Char] = List('a', 'b')
val indexed = chars.zipWithIndex // List(('a', 0), ('b', 1))
175

176. NESTEDDATA
def getFiles(date: LocalDate): List[String]
def getEvents(filename: String): List[Json]
def getUserId(event: Json): String
176

177. NESTEDDATA
def getFiles(date: LocalDate): List[String]
def getEvents(filename: String): List[Json]
def getUserId(event: Json): String
val filenames = getFiles(LocalDate.of(2016, 10, 10))
177

178. NESTEDDATA
def getFiles(date: LocalDate): List[String]
def getEvents(filename: String): List[Json]
def getUserId(event: Json): String
val filenames = getFiles(LocalDate.of(2016, 10, 10))
val events = filenames.map(file => getEvents(file))
178

179. NESTEDDATA
def getFiles(date: LocalDate): List[String]
def getEvents(filename: String): List[Json]
def getUserId(event: Json): String
val filenames = getFiles(LocalDate.of(2016, 10, 10))
val events = filenames.map(file => getEvents(file)) // List[List[Json]]
179

180. NESTEDDATA
def getFiles(date: LocalDate): List[String]
def getEvents(filename: String): List[Json]
def getUserId(event: Json): String
val filenames = getFiles(LocalDate.of(2016, 10, 10))
val events = filenames.map(file => getEvents(file)).flatten // List[Json]
180

181. FLATMAP
def getFiles(date: LocalDate): List[String]
def getEvents(filename: String): List[Json]
def getUserId(event: Json): String
val filenames = getFiles(LocalDate.of(2016, 10, 10))
val events = filenames.flatMap(file => getEvents(file)) // List[Json]
181

182. FLATMAP
def getFiles(date: LocalDate): List[String]
def getEvents(filename: String): List[Json]
def getUserId(event: Json): String
val filenames = getFiles(LocalDate.of(2016, 10, 10))
val events = filenames.flatMap(file => getEvents(file)) // List[Json]
val userIds = events.map(event => getUserId(event)) // List[String]
182

183. FLATMAP
def getFiles(date: LocalDate): List[String]
def getEvents(filename: String): List[Json]
def getUserId(event: Json): String
val userIds = getFiles(LocalDate.of(2016, 10, 10))
.flatMap(file => getEvents(file)) // List[Json]
.map(event => getUserId(event)) // List[String]
183

184. FLATMAP
def getFiles(date: LocalDate): List[String]
def getEvents(filename: String): List[Json]
def getUserId(event: Json): String
val userIds = getFiles(LocalDate.of(2016, 10, 10))
.flatMap(getEvents(_)) // List[Json]
.map(getUserId(_)) // List[String]
184

185. FLATMAP
def getFiles(date: LocalDate): List[String]
def getEvents(filename: String): List[Json]
def getUserId(event: Json): String
val userIds = getFiles(LocalDate.of(2016, 10, 10))
.flatMap(getEvents) // List[Json]
.map(getUserId) // List[String]
185

186. MAP,FILTER&FLATMAP
• Reach into the container
• List, Option, Try, Future, …
• Take the happy path
186

187. FOR-COMPREHENSIONS
def getFiles(date: LocalDate): List[String]
def getEvents(filename: String): List[Json]
def getUserId(event: Json): String
val userIds = getFiles(LocalDate.of(2016, 10, 10))
.flatMap(file => getEvents(file)) // List[Json]
.map(event => getUserId(event)) // List[String]
187

188. FOR-COMPREHENSIONS
def getFiles(date: LocalDate): List[String]
def getEvents(filename: String): List[Json]
def getUserId(event: Json): String
val userIds = getFiles(LocalDate.of(2016, 10, 10))
.flatMap(file => getEvents(file)) // List[Json]
.map(event => getUserId(event)) // List[String]
val userIds = for {
file <- getFiles(LocalDate.of(2016, 10, 10))
event <- getEvents(file)
} yield getUserId(file, event)
188

189. COLLECT
List result = new ArrayList();
for (Element element : elements) {
if (element instanceof SpecialElement) {
SpecialElement se = (SpecialElement) se;
if (accept(se))
result.add(transform(se));
}
}
189
https://ochafik.com/blog/?p=393

190. COLLECT
List result = new ArrayList();
for (Element element : elements) {
if (element instanceof SpecialElement) {
SpecialElement se = (SpecialElement) element;
if (accept(se))
result.add(transform(se));
}
}
val result = elements.collect {
case se: SpecialElement if accept(se) => transform(se)
}
190
https://ochafik.com/blog/?p=393

191. ACCUMULATION
def sum(numbers: List[Int])
191

192. ACCUMULATION
def sum(numbers: List[Int]) = {
var sum = 0
for (i <- numbers) sum += i
sum
}
192

193. RECURSION
def sum(numbers: List[Int]): Int = numbers match {
case Nil => 0
case head :: tail => head + sum(tail)
}
193

194. RECURSION
@tailrec
def sum(numbers: List[Int]): Int = numbers match {
case Nil => 0
case head :: tail => head + sum(tail)
}
194

195. RECURSION
def sum(numbers: List[Int]) = {
@tailrec
def loop(acc: Int, numbers: List[Int]): Int = numbers match {
case Nil => acc
case head :: tail => loop(acc + head, tail)
}
loop(0, numbers)
}
195

196. RECURSION-THEGOTOOFFP
196

197. FOLD
197

198. FOLD
• Initial value
• Accumulator
• Operator
198

199. FOLD
def sum(numbers: List[Int]) = {
@tailrec
def loop(acc: Int, numbers: List[Int]): Int = numbers match {
case Nil => acc
case head :: tail => loop(acc + head, tail)
}
loop(0, numbers)
}
199

200. FOLD
def sum(numbers: List[Int]) = {
@tailrec
def loop(acc: Int, numbers: List[Int]): Int = numbers match {
case Nil => acc
case head :: tail => loop(acc + head, tail)
}
loop(0, numbers)
}
def sum(numbers: List[Int]) = numbers.foldLeft(0)((acc, n) => acc + n)
200

201. FOLD
def sum(numbers: List[Int]) = {
@tailrec
def loop(acc: Int, numbers: List[Int]): Int = numbers match {
case Nil => acc
case head :: tail => loop(acc + head, tail)
}
loop(0, numbers)
}
def sum(numbers: List[Int]) = numbers.foldLeft(0)(_ + _)
201

202. EXERCISE5
202

203. LAZINESS,IMPLICITSANDDSLS

204. LAZINESS
• Streams
• Iterators
• Views
204

205. STREAMS
• Lazy sequence
• Values computed on demand first time
• Can be accessed many times
205

206. ITERATORS
• Iterate over elements one by one
• Use once
206

207. VIEWS
• Lazy transformations
• map, filter, etc.
• Use once
207

208. IMPLICITS
• Values / parameters / methods automagically inserted by compiler
208

209. IMPLICITS
val people: List[Person] = ...
val sortByName = people.sortBy(_.name)
209

210. IMPLICITS
val people: List[Person] = ...
val sortByName = people.sortBy(_.name)
def sortBy[B](f: A => B): List[B]
210

211. IMPLICITS
val people: List[Person] = ...
val sortByName = people.sortBy(_.name)
def sortBy[B](f: A => B)(implicit ord: scala.math.Ordering[B]): List[B]
211

212. IMPLICITS
val people: List[Person] = ...
val sortByName = people.sortBy(_.name)(Ordering[String])
def sortBy[B](f: A => B)(implicit ord: scala.math.Ordering[B]): List[B]
212

213. IMPLICITS
val clicks = Map("vg" -> 231232, "aftenposten" -> 158742)
213

214. IMPLICITS
val clicks = Map("vg" -> 231232, "aftenposten" -> 158742)
val clicks = Map(Tuple2(“vg”, 231232), Tuple2("aftenposten", 158742))
214

215. IMPLICITS
val clicks = Map("vg" -> 231232, "aftenposten" -> 158742)
val clicks = Map(Tuple2(“vg”, 231232), Tuple2("aftenposten", 158742))
implicit class ArrowAssoc[A](self: A) extends AnyVal {
def -> [B](b: B): Tuple2[A, B] = Tuple2(self, b)
}
215

216. DSLS
• Domain Specific Languages
• Decorators
• "Pimp my library"
• Jackson
• Kafka Streams
216

217. REPLACINGJSON4S
def providerId(event: JValue) = event "provider" "@id"
217

218. JACKSON
def providerId(event: JsonNode) = event.get("provider").get("@id")
218

219. JACKSON
implicit class RichJsonNode(node: JsonNode) {
def (fieldName: String): JsonNode =
Option(node get fieldName) getOrElse NullNode.instance
}
def providerId(event: JsonNode) = event "provider" "@id"
219

220. JACKSON
implicit class RichJsonNode(node: JsonNode) {
def (fieldName: String): JsonNode =
node path fieldName
}
def providerId(event: JsonNode) = event "provider" "@id"
220

221. 221

222. KAFKASTREAMS
val events = builder.stream(strings, json, sourceTopic)
val transformed = events.filter( … ).map( … )
transformed.to(strings, json, resultTopic)
222

223. KAFKASTREAMS
val events = builder.stream(strings, json, sourceTopic)
val transformed = events.filter( … ).map( … )
transformed.to(resultTopic) // ???
223

224. KAFKASTREAMS
class KStream[K, V] {
def to(keySerde: Serde[K], valSerde: Serde[V], topic: TopicName)
}
224

225. KAFKASTREAMS
object KafkaStreamsDSL {
implicit class RichKStream[K, V](stream: KStream[K, V]) {
def to(topic: TopicName)
}
}
225

226. KAFKASTREAMS
object KafkaStreamsDSL {
implicit class RichKStream[K, V](stream: KStream[K, V]) {
def to(topic: TopicName): Unit =
stream.to(keySerde, valSerde, topic)
}
}
226

227. KAFKASTREAMS
object KafkaStreamsDSL {
implicit class RichKStream[K, V](stream: KStream[K, V]) {
def to(topic: TopicName)
(implicit keySerde: Serde[K], valSerde: Serde[V]): Unit =
stream.to(keySerde, valSerde, topic)
}
}
227

228. KAFKASTREAMS
val events = builder.stream(strings, json, sourceTopic)
val transformed = events.filter( … ).map( … )
transformed.to(resultTopic) // ???
228

229. KAFKASTREAMS
val events = builder.stream(strings, json, sourceTopic)
val transformed = events.filter( … ).map( … )
import KafkaStreamsDSL._
implicit val strings = Serdes.string()
implicit val json = new JsonNodeSerde
transformed.to(resultTopic)
229

230. KAFKASTREAMS
val events = builder.stream(strings, json, sourceTopic)
val transformed = events.filter( … ).map( … )
import KafkaStreamsDSL._
implicit val strings = Serdes.string()
implicit val json = new JsonNodeSerde
transformed.~>(resultTopic)
230

231. KAFKASTREAMS
val events = builder.stream(strings, json, sourceTopic)
val transformed = events.filter( … ).map( … )
import KafkaStreamsDSL._
implicit val strings = Serdes.string()
implicit val json = new JsonNodeSerde
transformed ~> resultTopic
231

232. EVOLUTION
232

233. EVOLUTION
def extractUsers(iam: AmazonIdentityManagementClient, marker: String):
Seq[JsObject] = {
val result = iam.listUsers(new ListUsersRequest().withMarker(marker))
val batch = result.getUsers().asScala.map(userJson(iam, _))
val next: Seq[JsObject] =
if (result.getMarker() != null) {
extractUsers(iam, result.getMarker())
} else {
Seq[JsObject]()
}
batch ++ next
}
233

234. EVOLUTION
def extractGroups(iam: AmazonIdentityManagementClient, marker: String):
Seq[JsObject] = {
val result = iam.listGroups(new ListGroupsRequest().withMarker(marker))
val batch = result.getGroups().asScala.map(groupJson(_))
val next: Seq[JsObject] =
if (result.getMarker() != null) {
extractGroups(iam, result.getMarker())
} else {
Seq[JsObject]()
}
batch ++ next
}
234

235. EVOLUTION
def extract[A](fetch: String => A,
convert: A => Seq[JsObject],
isDone: A => Boolean,
getMarker: A => String): Seq[JsObject] = {
def loop(marker: String): Seq[JsObject] = {
val result = fetch(marker)
val batch = convert(result)
if (isDone(result)) batch else batch ++ loop(getMarker(result))
}
loop(null)
}
235

236. EVOLUTION
def extractUsers(iam: AmazonIdentityManagement) =
extract[ListUsersResult](
marker => iam.listUsers(new ListUsersRequest().withMarker(marker)),
result => result.getUsers.asScala.map(userJson(iam, _)),
_.isTruncated,
_.getMarker
)
def extractGroups(iam: AmazonIdentityManagement) =
extract[ListGroupsResult](
marker => iam.listGroups(new ListGroupsRequest().withMarker(marker)),
result => result.getGroups.asScala.map(groupJson),
_.isTruncated,
_.getMarker
)
236

237. EVOLUTION
type AwsListResult = {
def isTruncated(): java.lang.Boolean
def getMarker(): String
}
237

238. EVOLUTION
def extract[A](fetch: String => A,
convert: A => Seq[JsObject],
isDone: A => Boolean,
getMarker: A => String): Seq[JsObject] = {
def loop(marker: String): Seq[JsObject] = {
val result = fetch(marker)
val batch = convert(result)
if (isDone(result)) batch else batch ++ loop(getMarker(result))
}
loop(null)
}
238

239. EVOLUTION
def extract[A <: AwsListResult](fetch: String => A,
convert: A => Seq[JsObject]): Seq[JsObject] = {
def loop(marker: String): Seq[JsObject] = {
val result = fetch(marker)
val batch = convert(result)
if (result.isTruncated()) batch ++ loop(result.getMarker()) else batch
}
loop(null)
}
239

240. EVOLUTION
def extractUsers(iam: AmazonIdentityManagement) =
extract(
marker => iam.listUsers(new ListUsersRequest().withMarker(marker)),
result => result.getUsers.asScala.map(userJson(iam, _))
)
def extractGroups(iam: AmazonIdentityManagement) =
extract(
marker => iam.listGroups(new ListGroupsRequest().withMarker(marker)),
result => result.getGroups.asScala.map(groupJson)
)
240

241. EVOLUTION
def extract[A <: AwsListResult](fetch: String => A,
convert: A => Seq[JsObject]): Seq[JsObject] = {
def loop(marker: String): Seq[JsObject] = {
val result = fetch(marker)
val batch = convert(result)
if (result.isTruncated()) batch ++ loop(result.getMarker()) else batch
}
loop(null)
}
241

242. EVOLUTION
def extract[A <: AwsListResult, B](fetch: String => A)
(extract: A => java.util.List[B])
(implicit toJson: B => JsObject): Seq[JsObject] =
def loop(marker: String): Seq[JsObject] = {
val result = fetch(marker)
val batch = extract(result).asScala.map(toJson)
if (result.isTruncated()) batch ++ loop(result.getMarker()) else batch
}
loop(null)
}
242

243. EVOLUTION
def extractUsers() = extract(
marker => iam.listUsers(new ListUsersRequest().withMarker(marker))
)(_.getUsers)
def extractGroups() = extract(
marker => iam.listGroups(new ListGroupsRequest().withMarker(marker))
)(_.getGroups)
243

244. EVOLUTION
def extractUsers() = extract(users)(_.getUsers)
def extractGroups() = extract(groups)(_.getGroups)
def users(marker: String) =
iam.listUsers(new ListUsersRequest().withMarker(marker))
def groups(marker: String) =
iam.listGroups(new ListGroupsRequest().withMarker(marker))
244

245. ASYNC
245

246. ASYNC
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): List[Json]
246

247. ASYNC
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): List[Json]
val content = getFile(LocalDate.of(2016, 10, 10))
val events = ???
247

248. ASYNC
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): List[Json]
val content = getFile(LocalDate.of(2016, 10, 10))
content.onComplete {
}
248

249. ASYNC
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): List[Json]
val content = getFile(LocalDate.of(2016, 10, 10))
content.onComplete { res =>
res match {
case Success(json) => doSomething(json)
case Failure(ex) => fallbackLogic(ex)
}
}
249

250. ASYNC
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): List[Json]
val content = getFile(LocalDate.of(2016, 10, 10))
content.onComplete {
case Success(json) => doSomething(json)
case Failure(ex) => fallbackLogic(ex)
}
250

251. ASYNC
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): List[Json]
val content = getFile(LocalDate.of(2016, 10, 10))
content.onComplete {
case Success(json) => doSomething(json)
case Failure(ex) => fallbackLogic(ex)
}
val events = ???
251

252. MAP
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): List[Json]
val content = getFile(LocalDate.of(2016, 10, 10))
val events = content.map(json => parseEvents(json))
252

253. MAP
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): List[Json]
val content = getFile(LocalDate.of(2016, 10, 10))
val events = content.map(json => parseEvents(json)) // Future[List[Json]]
253

254. MAP
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): List[Json]
val content = getFile(LocalDate.of(2016, 10, 10))
val events = content.map(json => parseEvents(json)) // Future[List[Json]]
Await.result(events, Duration.Inf)
254

255. MAP
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): Future[List[Json]]
val content = getFile(LocalDate.of(2016, 10, 10))
val events = content.map(json => parseEvents(json))
// Future[Future[List[Json]]]
255

256. FLATMAP
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): Future[List[Json]]
val content = getFile(LocalDate.of(2016, 10, 10))
val events = content.flatMap(json => parseEvents(json)) // Future[List[Json]]
256

257. FOR-COMPREHENSIONS
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): Future[List[Json]]
val content = getFile(LocalDate.of(2016, 10, 10))
val events = content.flatMap(json => parseEvents(json))
257

258. FOR-COMPREHENSIONS
def getFile(date: LocalDate): Future[String]
def parseEvents(json: String): Future[List[Json]]
val content = getFile(LocalDate.of(2016, 10, 10))
val events = content.flatMap(json => parseEvents(json))
val events = for {
json <- getFile(LocalDate.of(2016, 10, 10))
events <- parseEvents(json)
} yield events
258

259. PARALLELLISM
• Futures for-comprehension (flatMap) vs zip/zipWith vs sequence
• traverse (parallel map)
259

260. WRAPUPANDQA

261. IMPERATIVEVSFUNCTIONAL
• Imperative : Change state
• Functional Programming (FP) : Compute new values
261

262. OBJECT-ORIENTEDVSFUNCTIONAL
• OO: Objects = state + behavior
• FP: Data structures + functions
262

263. OO+FP
• Scala = Hybrid FP + OO
• Leans towards FP “in the small”
• OO for “programming in the large”
263

264. DON’TBECUTE
• Optimize for readability
• Find the Scala level that works for your team
• The language grows with your understanding
• of Scala, and of FP
264

265. QA
• Questions?
• Anything you want to dive deeper into?
265

266. THANKYOU!
@fredriv / fredrik.vraalsen@schibsted.com