Talk presented at Codemotion Madrid 2017. Kotlin in a live production environment from early 2017, in microservices using a Java platform in Tuenti, Discussions on risks and experiences months after.

1. Poniendo
by @andres_viedma
en producción
A palos
MAD · NOV 24-25 · 2017

2. Andrés ViedmaAndrés Viedma
@andres_viedma@andres_viedma

3. 01 KOTLIN

5. Null safety
fun printStringLength(maybeString: String?) {
// maybeString.length would not compile
if (maybeString != null) {
// maybeString cannot be null now, it's a String
println(maybeString.length)
} else {
println("<empty>")
}
}
”My billion dollars mistake”
Tony Hoare

6. fun printStringLength1(maybeString: String?) {
maybeString?.let { s -> println(s) }
}
fun printStringLengthOrEmpty(maybeString: String?) {
println(maybeString?.length ?: "<empty>")
}
Null safety

7. A small immutable Kotlin class
data class TokenInfo(
val tokenType: String = “auth”,
val identity: String
val expiration: Int? = null
)

8. Constructor with Properties
class TokenInfo(
val tokenType: String,
val identity: String
(…)
)
public final class TokenInfo {
private final String tokenType;
private final String identity;
(…)
public TokenInfo(
String tokenType,
String identity,
(…)) {
this.tokenType = tokenType;
this.identity = identity;
(…)
}
public final String getTokenType() {
return tokenType;
}
public final String getIdentity() {
return identity;
}
}

9. Getters and Setters
class TokenInfo(
val tokenType: String,
val identity: String
(…)
)
public final class TokenInfo {
private final String tokenType;
private final String identity;
(…)
public TokenInfo(
String tokenType,
String identity,
(…)) {
this.tokenType = tokenType;
this.identity = identity;
(…)
}
public final String getTokenType() {
return tokenType;
}
public final String getIdentity() {
return identity;
}
}

10. Named arguments and optional values
class TokenInfo(
val tokenType: String = "auth",
val identity: String,
val expiration: Int? = null
)
val token = TokenInfo(identity = "xxx")
Immutable classes with
optional fields?
Constructors with lots of
parameters
Builder object

11. Data classes
data class TokenInfo(
val tokenType: String,
val identity: String
(…)
)
public final class TokenInfo {
(…)
public String toString() { (…) }
public int hashCode() { (…) }
public boolean equals(Object var1) { (…) }
public final TokenInfoId copy(String tokenType,
String identity) {
(…)
}
public final String component1() { (…) }
public final String component2() { (…) }
}
Immutability
made easier

12. Collections improvements
List<Person> persons = Arrays.asList(
new Person("Sansa", "Stark"),
new Person("Jon", "Snow"));
List<String> personNames = persons.stream()
.map(p -> p.getName() + " " + p.getSurname())
.collect(Collectors.toList());
val persons = listOf(
Person("Sansa", "Stark"),
Person("Jon", "Snow"))
val personNames = persons
.map { p -> "${p.name} ${p.surname}" }
Extension functions

13. Collections improvements
List<Integer> result = list.stream()
.flatMap(o -> o.isPresent() ?
Stream.of(o.get()) : Stream.empty())
.collect(Collectors.toList());
val result = list.filter { it != null }
List<Integer> result = list.stream()
.flatMap(o → o.map(Stream::of)
.orElseGet(Stream::empty))
.collect(Collectors.toList());
List<Integer> result = list.stream()
.flatMap(Optional::stream)
.collect(Collectors.toList());

14. String Interpolation
List<Person> persons = Arrays.asList(
new Person("Sansa", "Stark"),
new Person("Jon", "Snow"));
List<String> personNames = persons.stream()
.map(p -> p.getName() + " " + p.getSurname())
.collect(Collectors.toList());
val persons = listOf(
Person("Sansa", "Stark"),
Person("Jon", "Snow"))
val personNames = persons
.map { p -> "${p.name} ${p.surname}" }

15. Type Inference
val persons = listOf(
Person("Sansa", "Stark"),
Person("Jon", "Snow"))
val personNames = persons
.map { p -> "${p.name} ${p.surname}" }
List<Person> persons = Arrays.asList(
new Person("Sansa", "Stark"),
new Person("Jon", "Snow"));
List<String> personNames = persons.stream()
.map(p -> p.getName() + " " + p.getSurname())
.collect(Collectors.toList());

16. Gotcha! Now the idea is trapped inside your head

17. Gotcha! Now the idea is trapped inside your head

18. Gotcha! Now the idea is trapped inside your head

19. 02 LET'S DO IT!

20. Tell the team!
The conformist

21. Tell the team!
The conformist The idealist

22. Tell the team!
The conformist The idealist The responsible

23. Tell the team!
The conformist The idealist The responsible
AGGG ROOO RAGGAGGG ROOO RAGG
ROOOOOOOGHH!ROOOOOOOGHH!

24. What about the rest of the company?

25. Option 1...

26. Option 2: Talk to them

27. ●
Can affect development time
●
Misunderstandings can increase bug rate
●
Service responsibility is not fixed
Not just YOUR team
Learning cost

28. ●
Learning curve very smooth
●
On doubt, use Java style and methods
●
Not a real paradigm change
●
Same libraries and concepts
Learning cost ® BUT...

29. ●
Good documentation
●
Short library
●
Is there a general interest in Kotlin in the company?
Kotlin community
Android devs pushing for a change
Learning cost ® BUT... (2)

30. ●
It's production!
●
New technology, may have bugs
●
Adds code “behind the courtains”
●
Any weird behaviour affecting memory, garbage collection...
Can affect Performance

31. ●
Same Java VM
●
You can see compiled bytecode
●
Decompile problematic code to Java and tune it
●
Start a component in Java and then convert it to Kotlin
Can affect Performance ® BUT...

32. ●
Extension functions are just a trick, no overhead
●
Null checks are a small runtime overhead
●
Platform and base libraries are the sane
●
Kotlin library overhead not important for backend
Can affect Performance ® BUT... (2)

33. ●
Increased build time
●
Find equivalent tools
●
Adaptation to those tools
Tooling problems

34. ●
Same IDE: IntelliJ, Eclipse...
●
Same build tools: Maven, Gradle...
●
In a microservices architecture build time not so critical
Seconds?
Tooling problems ® BUT...

35. ●
What if Kotlin stops being “cool”?
●
What if nobody uses it anymore?
●
What if it just dissapears?
Supported / created by Jetbrains
Long-term vision

36. Long-term vision ® BUT...

37. 03 10 MONTHS
LATER...

38. ●
Development time basically the same
●
Code Reviews more interesting!
●
Our Java platform was 100% compatible
Learning cost?

39. ●
Rest of the company?
4 teams doing services in Kotlin
Kotlin now official in the company for Android
Learning cost?

40. final vs. open
Some Java libraries rely on
dinamically creating subclasses
●
Interceptors and other injection “black magic”
Spring, Guice…
●
Mocks: Mockito, Spock

41. Compiler plugins
●
All-open: Make classes open
Shortcut: Spring
●
No-args: Create a no-args constructor
Shortcut: JPA
Beware!: only by annotations

42. Compiler plugins ® All-open not enough
●
@Transactional problem (if no class annotation)
Explicit open class and methods
●
Mocks?
Mockito 2.1.0 “inline mocks”: “incubating”
Kotlin-runner library: explicit packages

43. Compiler plugins ® No-args not enough
●
Object Mapper libraries
Explicit no-args constructor
●
Spock tests
Named parameters don’t work from Java / Groovy

44. const val ONE = 1 // MyObject(1) NO OBJECTS ALLOWED
// Translated to: public static final
class Constants {
companion object {
const val TWO = 2 // MyObject(2) NO OBJECTS ALLOWED
// Translated to: inlined
val THREE = MyObject(3) // Translated to private static
// + Companion class with getter
@JvmField val FOUR = MyObject(4) // Translated to public static final
}
}
Constants: too many options?
https://blog.egorand.me/where-do-i-put-my-constants-in-kotlin/

45. val description: String (type after identifier)

46. val description: String (type after identifier)

47. Can affect Performance?

48. ●
Eclipse with Kotlin and Groovy tests just don’t work
●
Eclipse incremental compilation a bit slow
●
Some crashes when updating IntelliJ plugin
●
Incremental build disabled by default in some versions
Maven+Gradle
●
Checkstyle, Findbugs…
Tooling problems?

49. ●
Eclipse with Kotlin and Groovy tests just don’t work
●
Eclipse incremental compilation a bit slow
●
Some crashes when updating IntelliJ plugin
●
Incremental build disabled by default in some versions
Maven+Gradle
●
Checkstyle, Findbugs…
Tooling problems?

50. 04 Beyond
the basics

51. Functional features
fun processPersonName(person: Person?, processor: (String) -> Boolean) =
processor(
when(person) {
null -> "null"
is AnonymousPerson -> "anonymous"
else -> when {
person.isBoss -> "a boss"
else -> "the simple ${person.name}"
}
}
)

52. ●
Not 100% functional
●
Higher kind types
●
Typeclasses
●
Proposal (KEEP) in discussion to add them, by @raulraja
●
Kategory library - http://kategory.io/
Functional paradigm?

53. Black magic
companion { [constants: USER_ID, PRODUCTS, OK_RESULT...) }
val storeCatalogStub = Stub<StoreCatalog> {
getProductsForUserId(USER_ID) <= PRODUCTS
}
val storeMock = Mock<ProductStore>()
val purchaseHistoryMock: PurchaseHistory = Mock()
fun `Purchase correct product available in the store`() {
given("A valid user") {
userService.isValidUser(USER_ID) <= true
} `when`("The user tries to do the purchase") {
purchaseOperation.perform(USER_ID, PRODUCT_ID)
} then("Product is purchased") {
1 * storeMock.purchaseProduct(USER_ID, PRODUCT_ID, null.not()) <= OK_RESULT
} and("Operation is logged") {
(1..any) * purchaseHistoryMock.logProductPurchased(USER_ID, PRODUCT_ID, any())
} and("No more interactions") {
0 * any
}
}

54. Black magic
companion { [constants: USER_ID, PRODUCTS, OK_RESULT...) }
val storeCatalogStub = Stub<StoreCatalog> {
getProductsForUserId(USER_ID) <= PRODUCTS
}
val storeMock = Mock<ProductStore>()
val purchaseHistoryMock: PurchaseHistory = Mock()
fun `Purchase correct product available in the store`() {
given("A valid user") {
userService.isValidUser(USER_ID) <= true
} `when`("The user tries to do the purchase") {
purchaseOperation.perform(USER_ID, PRODUCT_ID)
} then("Product is purchased") {
1 * storeMock.purchaseProduct(USER_ID, PRODUCT_ID, null.not()) <= OK_RESULT
} and("Operation is logged") {
(1..any) * purchaseHistoryMock.logProductPurchased(USER_ID, PRODUCT_ID, any())
} and("No more interactions") {
0 * any
}
}
Lambda param after
parenthesis
Code generation
(compiler plugin)

55. Black magic
companion { [constants: USER_ID, PRODUCTS, OK_RESULT...) }
val storeCatalogStub = Stub<StoreCatalog> {
getProductsForUserId(USER_ID) <= PRODUCTS
}
val storeMock = Mock<ProductStore>()
val purchaseHistoryMock: PurchaseHistory = Mock()
fun `Purchase correct product available in the store`() {
given("A valid user") {
userService.isValidUser(USER_ID) <= true
} `when`("The user tries to do the purchase") {
purchaseOperation.perform(USER_ID, PRODUCT_ID)
} then("Product is purchased") {
1 * storeMock.purchaseProduct(USER_ID, PRODUCT_ID, null.not()) <= OK_RESULT
} and("Operation is logged") {
(1..any) * purchaseHistoryMock.logProductPurchased(USER_ID, PRODUCT_ID, any())
} and("No more interactions") {
0 * any
}
}
Operator overloading
Reified generics
Extension functions
https://github.com/Koxalen

56. More...
●
Coroutines
●
Type aliases
●
Sealed classes
●
Delegated properties
●
Inline functions

57. Android
●
Anko library
●
Consider performance and limits
7k methods (65k methods limit): 10%
380 KB
Compilation slower

58. Multi-platform
●
Javascript
Kotlin wrapper for ReactJS
●
Native
Kotlin plugin for CLion
Kotlin/Native iOS support
Not only the JVM!
KotlinConf app fully made with Kotlin

59. SO WHAT???05

60. Yay or Nay?
●
Controlled risk, but… worth it?
●
What’s the benefit?
Mostly syntatic sugar
Productivity really improved???

61. Yay or Nay?
●
Controlled risk, but… worth it?
●
What’s the benefit?
Mostly syntatic sugar
Productivity really improved???
How about thinking about PEOPLE
instead of PRODUCTS?

62. It’s all about LEARNING
and MOTIVATION

64. Questions?
Andrés Viedma · @andres_viedma