"The joy of Scala" - Maxim Novak / Wix Around eight years ago I started my journey as a developer. Since then, I've played around with many languages and thought that C# offers the best developer productivity. After joining Wix two years ago, I was exposed to the amazing world of Scala and Functional Programming and never looked back. In Scala the code is much more concise, less ceremonious, immutable by default, combines functional with object oriented, seamlessly interoperates with Java, and many software engineering patterns are already baked into the language. Most importantly - Scala is FUN! By the end of the session you too will, hopefully, convert to Scala and never look back. Recording of the lecture (Hebrew) - https://youtu.be/TcnYTwff2xU

1. The Joy of
Maxim Novak
@maximnovakmaximn@wix.com https://github.com/maximn
Or : Why I love Scala

2. The Joy of
Maxim Novak
@maximnovakmaximn@wix.com https://github.com/maximn
Or : Why I love Scala

3. Hi
I’m Maxim Novak.
• Working on Wix’s back-end
• 9 years in the software industry
• 3 years avid Scala advocate

4. Scala is the better Java.

5. Scala is the better Java.

6. Simple concepts
Big impact

7. Why I Scala
Conciseness

8. public class Checkout {
private double tax;
public Checkout(double tax) {
this.tax = tax;
}
double total(final List<Product> products) {
double total = 0.0;
for (Product product : products) {
total += product.getPrice();
}
return total * tax;
}
}
Java (7) Checkout class

9. public class Checkout {
private double tax;
public Checkout(double tax) {
this.tax = tax;
}
double total(final List<Product> products) {
return products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax;
}
}
Java (8) Checkout class

10. public class Checkout {
private double tax;
public Checkout(double tax) {
this.tax = tax;
}
double total(final List<Product> products) {
return products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax;
}
}
Public by default

11. Public by default
class Checkout {
private double tax;
public Checkout(double tax) {
this.tax = tax;
}
double total(final List<Product> products) {
return products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax;
}
}

12. class Checkout {
private double tax;
public Checkout(double tax) {
this.tax = tax;
}
double total(final List<Product> products) {
return products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax;
}
}
No need for semi-colons

13. No need for semi-colons
class Checkout {
private double tax
public Checkout(double tax) {
this.tax = tax
}
double total(final List<Product> products) {
return products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax
}
}

14. class Checkout {
private double tax
public Checkout(double tax) {
this.tax = tax
}
double total(final List<Product> products) {
return products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax
}
}
Concise constructor and fields

15. Concise constructor and fields
class Checkout(tax: Double) {
double total(final List<Product> products) {
return products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax
}
}

16. class Checkout(tax: Double) {
double total(final List<Product> products) {
return products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax
}
}
Return last statement by default

17. Return last statement by default
class Checkout(tax: Double) {
double total(final List<Product> products) {
products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax
}
}

18. class Checkout(tax: Double) {
double total(final List<Product> products) {
products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax
}
}
Method arguments are final by default
And the Name comes before the Type

19. Method arguments are final by default
And the Name comes before the Type
class Checkout(tax: Double) {
def total(products: Seq[Product]): Double = {
products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax
}
}

20. class Checkout(tax: Double) {
def total(products: Seq[Product]): Double = {
products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax
}
}
Type Inference

21. Type Inference
class Checkout(tax: Double) {
def total(products: Seq[Product]) = {
products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax
}
}

22. class Checkout(tax: Double) {
def total(products: Seq[Product]) = {
products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax
}
}
Remove more boilerplate

23. class Checkout(tax: Double) {
def total(products: Seq[Product]) =
products.map(_.getPrice).sum * tax
}
P P P P 1 3 7 4 15
.map(_.getPrice) .sum
Remove more boilerplate

24. class Checkout(tax: Double) {
def total(products: Seq[Product]) =
products.map(_.getPrice).sum
* tax
}
Scala
public class Checkout {
private double tax;
public Checkout(double tax) {
this.tax = tax;
}
double total(final List<Product>
products) {
return products
.stream()
.mapToDouble(Product::getPrice)
.sum() * tax;
}
}
Java

25. class Checkout(tax: Double) {
def total(products: Seq[Product]) =
products.map(_.getPrice).sum
* tax
}
Scala
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World");
}
}
Java

26. Immutable by default
Easier to use = always thread safe = testable

27. Immutable by default
Prefer vals, immutable objects, and methods without side effects.
Reach for them first.
Use vars, mutable objects, and methods with side effects when
you have a specific need and justification for them.
- Programming in Scala By Martin Odersky, Lex Spoon, Bill Venners
“
”
http://www.yegor256.com/2014/06/0
9/objects-should-be-immutable.html
Easier to use = always thread safe = testable

28. Immutability
Set<Date> set = new HashSet<>();
Date date = new Date(2);
set.add(date);
date.setTime(4);
System.out.println(set.contains(date));
Easier to use = always thread safe = testable
http://www.yegor256.com/2014/06/09/
objects-should-be-immutable.html
HashCode Object
1
2
3
4
...
...
n
date
date

29. Domain Objects

30. public class Product {
public Product(String name, double price) {
this.name = name;
this.price = price;
}
private String name;
private double price;
public double getPrice() {
return price;
}
public String getName() {
return name;
}
@Override
public String toString() {
return "Product{" +
"name='" + name + ''' +
", price=" + price +
'}';
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass())
return false;
Product product = (Product) o;
if (Double.compare(product.price, price) != 0)
return false;
return name != null ?
name.equals(product.name) : product.name ==
null;
}
@Override
public int hashCode() {
int result;
long temp;
temp = Double.doubleToLongBits(price);
result = (int) (temp ^ (temp >>> 32));
result = 31 * result + (name != null ?
name.hashCode() : 0);
return result;
}
}
public void setPrice(double price) {
this.price = price;
}
public void setName(String name) {
this.name = name;
}

31. Case Classes
case class Product(name: String, price: Double)
Less code = Less bugs = Readable code = Easier to maintain
Indeed, the ratio of time spent reading versus writing is well over 10 to 1.
We are constantly reading old code as part of the effort to write new code.
...[Therefore,] making it easy to read makes it easier to write.
- Robert C. Martin, Clean Code: A Handbook of Agile Software Craftsmanship
“
”

32. Case Classes
case class Product(name: String, price: Double)
What else?
val book = Product("Book", 42)
val discountedBook = book.copy(price = 32)

33. Static Types Inference
Promotes better naming over type declaration
val i = 8
val s = "bar"
val withExplicitType: String = "baz"
val product = new Product(“name", 18)
val seq = Seq(1, 2, 3)
val withExplicitType: String = 8
Error:(4, 34) type mismatch;
found : Int(8)
required: String
val withExplicitType: String = 8

34. Static Types Inference
Promotes better naming over type declaration
val i = 8
val s = "bar"
val withExplicitType: String = "baz"
val product = new Product(“name", 18)
val seq = Seq(1, 2, 3)
def withString(s: String) = …
withString(i)
Error:(29, 16) type mismatch;
found : Int
required: String
withString(i)
^

35. private def add(a: Int, b: Int) = a + b
def add(a: Int, b: Int): Int = a + b
Static Types Inference
Promotes better naming over type declaration

36. Clarity &
Comprehension

37. Why I Scala
1. Use types to understand functions

38. interface Calculator {
Double divideOneBy(Integer divisor)
}
calculator.divideOneBy(0);
null ArithmeticException Double.NaN
What’s the result ?

39. Meet Scala Options
A better way for handling NULLs
Option [ T ]
None Some [ T ]

40. trait Calculator {
def divideOneBy(i: Int): Option[Double]
}
calculator.divideOneBy(0) == None
calculator.divideOneBy(2) == Some(0.5)
Meet Scala Options
A better way for handling NULLs

41. Meet Scala Options
val result: Option[Double]=calculator.divideOneBy(...)
var halfResult: Double = null
if (result.isDefined) {
halfResult = result.get / 2
}
else { ??? }
Imperative Style

42. val result: Option[Double] = calculator.divideOneBy(...)
val halfResult = result.map(r => r / 2)
Meet Scala Options
Functional style

43. val result: Option[Double] = calculator.divideOneBy(...)
val halfResult = result.map(_ / 2)
Meet Scala Options
Functional style

44. val productPhotoUrl: Option[String] = ...
val photoUrl: String =
productPhotoUrl.getOrElse("http://site.com/defaultProductImage.jpg")
Meet Scala Options
Default Values

45. What You Can Do with Options
val default: Option[String] = ...
val fallback: Option[String] = ...
val url = default.orElse(fallback)
Fallback

46. Java Libraries
Working with Java? Just wrap it with an Option
Option(null) == None
Option(obj) == Some(obj)

47. def javaApi(): SomeType = ...
val result = Option(javaApi())
NullPointerException – Never Again
Java Libraries
Working with Java? Just wrap it with an Option

48. Meet Scala’s Try
The flow is clear when it comes to Exceptions
Try [ T ]
Failure Success [ T ]

49. Why I Scala
1. Use types to understand functions
2. Elegant flow

50. For Comprehension
case class Photo(url: String)
case class Product(name: String, photo: Photo)
def photoUrl(product: Product) = {
var url: String = null
if (product != null) {
if (product.photo != null) {
if (product.photo.url != null) {
url = product.photo.url
}
}
}
url
}

51. case class Photo(url: String)
case class Product(name: String, photo: Photo)
def photoUrl(product: Product) = {
var url: String = null
if (product != null) {
if (product.photo != null) {
if (product.photo.url != null) {
url = product.photo.url
}
}
} url
}
case class Photo(url: Option[String])
case class Product(name: String, photo: Option[Photo])
def photoUrl(productOpt: Option[Product]) =
for {
product <- productOpt
photo <- product.photo
url <- photo.url
} yield url

52. Why I Scala
1. Use types to understand functions
2. Elegant flow
3. Powerful Pattern matching

53. Pattern Matching
A more powerful switch/case
val x: Any = ...
x match {
case 1 => "It's an integer 1"
case "1" => "It's a String "1""
case b: Boolean => "It's the a boolean : " + b.toString
case i: Int if i > 0 => "It's a positive Integer : " + i
case _: String => "It's a String, don’t care the value"
case _: Float | _: Double => "Something numeric"
case _ => "Didn't match any condition"
}

54. val obj: AnyRef = ...
obj match {
case Product(_, 0) =>
println("FREE! Don’t care about the name")
case Product(name, price) =>
println(name + " cost" + price)
}
Pattern Matching
Extracting Case-Classes
case class Product(name: String, price: Double)

55. val url: java.net.URL = ...
url match {
case HTTP(address) => "HTTP! It’s : " + address
case _ => "Unknown protocol"
}
object HTTP {
def unapply(url: URL): Option[String] =
if (url.getProtocol == "http") Some(url.toString)
else None
}
Custom Extractors
Make your code cleaner by extracting the how to’s

56. val url: java.net.URL = ...
url match {
case HTTP(address) => "HTTP! It’s : " + address
case FTP(address) => "FTP! It’s : " + address
case File(path) => "File! It’s : " + path
case CustomProtocol(foo, bar) =>
"Custom! It’s : " + foo + "/" + bar
case _ => "Unknown protocol"
}
Custom Extractors
Make your code cleaner by extracting the how to’s

57. Why I Scala
1. Use types to understand functions
2. Elegant flow
3. Powerful Pattern matching
4. Awesome Parameters

58. Default Parameters
class DatabaseConnection {
public DatabaseConnection(String host,
int port,
Credentials credentials) {}
}
Constructor overloading

59. Default Parameters
class DatabaseConnection {
public DatabaseConnection(String host,
int port,
Credentials credentials) {}
public DatabaseConnection(String host,
Credentials credentials) {
this(host, 3306, credentials); }
}
Constructor overloading

60. Default Parameters
class DatabaseConnection {
public DatabaseConnection(String host,
int port,
Credentials credentials) {}
public DatabaseConnection(String host,
Credentials credentials) {
this(host, 3306, credentials); }
public DatabaseConnection(Credentials credentials) {
this("localhost", credentials); }
}
Constructor overloading

61. Default Parameters
class DatabaseConnection {
public DatabaseConnection(String host,
int port,
Credentials credentials) {}
public DatabaseConnection(String host,
Credentials credentials) {
this(host, 3306, credentials); }
public DatabaseConnection(Credentials credentials) {
this("localhost", credentials); }
public DatabaseConnection() { this(Credentials.empty); }
}
Constructor overloading

62. Default Parameters
class DatabaseConnectionBuilder {
private String host = "localhost";
private int port = 3306;
private Credentials credentials = Credentials.empty
public DatabaseConnectionBuilder withHost(int port) {
this.host = host; return this; }
public DatabaseConnectionBuilder withPort(int port) {
this.port = port; return this; }
public DatabaseConnectionBuilder withCredentials(Credentials credentials) {
this.credentials = credentials; return this; }
public DatabaseConnection build() {
return new DatabaseConnection(host, port, credentials);
}
}
Builder Pattern

63. Default Parameters
class DatabaseConnection(host: String = "localhost",
port: Int = 3306,
credentials: Credentials = Credentials.empty)

64. Default Parameters
class DatabaseConnection(host: String = "localhost",
port: Int = 3306,
credentials: Credentials = Credentials.empty)
new DatabaseConnection("otherhost.com")

65. Default Parameters
class DatabaseConnection(host: String = "localhost",
port: Int = 3306,
credentials: Credentials = Credentials.empty)
new DatabaseConnection(port = 3030)

66. Named Parameters
new File(path).setExecutable(true, false)

67. Named Parameters
boolean executable = true;
boolean ownerOnly = false;
new File(path).setExecutable(executable, ownerOnly);

68. Named Parameters
new File(path).setExecutable(executable = true, ownerOnly = false)

69. Why I Scala
1. Use types to understand functions
2. Elegant flow
3. Powerful Pattern matching
4. Awesome Parameters
5. Easier Strings

70. String Interpolation
More readable, Use $ for variables
val name = "Max"
val lang = "Scala"
val desc = s"Hello $name. $lang is awesome!"
Hello Max. Scala is awesome!

71. Quotes & Multiline
More readable, Easier to implement
val withQuotes =
"""Now I can use "quotes" without escaping"""
val multiline =
"""{
"firstName": "John",
"lastName": "Smith",
"age": 25
}"""

72. Why I Scala
1. Use types to understand functions
2. Elegant flow
3. Powerful Pattern matching
4. Awesome Parameters
5. Easier Strings
6. DSLs

73. Implicit Classes (extension methods)
import java.io.File
implicit class FileOps(val file: File) extends AnyVal {
...
def isClass: Boolean = file.isFile &&
file.getName.endsWith(".class")
...
}

74. Implicit Classes (extension methods)
import scala.tools.nsc.classpath.FileUtils.FileOps
val f = new File(...)
val isClass = f.isClass

75. Implicit Classes (extension methods)

76. Implicit Classes (extension methods)
1.to(10)
Range.Inclusive(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

77. Infix Notation
String c = "foo".concat("bar");
String p = "foo" + "bar";

78. Infix Notation
val c = "foo" concat "bar"
“The binary operation E op E` is always interpreted as the
method call E.op(E`) “
-- Martin Odersky (Scala By Example)
https://www.scala-lang.org/old/sites/default/files/linuxsoft_archives/docu/files/ScalaByExample.pdf

79. Implicit Classes & Infix Notation
1 to 10
for (i <- 1 to 10) {
...
}

80. DSL Made Easy
specs2 example
class SampleTest extends Specification {
"The 'Hello world' string" should {
"contain 11 characters" >> {
"Hello world" must haveSize(11)
}
}
}

81. DSL Made Easy
specs2 example

82. FUN & PROFIT
http://stackoverflow.com/research/developer-survey-2016

83. FUN & PROFIT
http://stackoverflow.com/research/developer-survey-2016

84. First Steps

85. You’re not alone
Adopted by:
… and a rapidly growing community

86. Migrating from Java
You can do it! Things working for you:
EASY to start

87. Migrating from Java
You can do it! Things working for you:
All Java libraries that you know and love
work in Scala too

88. Migrating from Java
You can do it! Things working for you:
You can start imperative and
move to functional, decide
where you want to be

89. Migrating from Java
There are caveats. Things working against you:
(Too much?) freedom
in programming style
http://www.lihaoyi.com/post/StrategicScalaStylePrincipleofLeastPower.html

90. Migrating from Java
There are caveats. Things working against you:
Slower
compile time

91. Migrating from Java
There are caveats. Things working against you:
Less tooling

92. Migrating from Java
There are caveats. Things working against you:
Recruiting

93. Java
Step 1
Tests in Scala
Scala
Step 2
Convert class to JALA,
make it compile,
refactor

94. Java
Step 1
Tests in Scala
Scala
Step 2
Convert class to JALA,
make it compile,
refactor
Step 3
scala.collections.
JavaConversions._
Step 4
@BeanProperty
Annotation

95. Java
Step 1
Tests in Scala
Scala
Step 2
Convert class to JALA,
make it compile,
refactor
Step 3
scala.collections.
JavaConversions._
Step 4
@BeanProperty
Annotation
Step 5
Preserve Git
history

96. Java
Step 1
Tests in Scala
Scala
Step 2
Convert class to JALA,
make it compile,
refactor
Step 3
scala.collections.
JavaConversions._
Step 4
@BeanProperty
Annotation
Step 5
Preserve Git
history

97. Java
Step 1
Tests in Scala
Scala
Step 2
Convert class to JALA,
make it compile,
refactor
Step 3
scala.collections.
JavaConversions._
Step 4
@BeanProperty
Annotation
Step 5
Preserve Git
history

98. Wanna Learn More?
https://twitter.github.io/scala_school/
http://danielwestheide.com/scala/neophytes.html
http://twitter.github.io/effectivescala/
https://www.scala-exercises.org/std_lib/asserts
Advanced Topics
• Multiple inheritance
• Implicits
• Macros
• Functional libraries

99. Thank You!
Any Questions?
Maxim Novak
@maximnovakmaximn@wix.com https://github.com/maximn