Poniendo Kotlin en producción a palos (Kotlin in production, the hard way)

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

Andrés ViedmaAndrés Viedma
@andres_viedma@andres_viedma

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

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

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

Constructor with Properties
class TokenInfo(
val tokenType: 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;
}
}

Getters and Setters
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;
}
}

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

Data classes
data 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

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

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

String Interpolation

Type Inference

Gotcha! Now the idea is trapped inside your head

Tell the team!
The conformist The idealist

Tell the team!
The conformist The idealist The responsible

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

What about the rest of the company?

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

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

●
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)

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

●
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...

●
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)

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

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

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

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

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

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

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

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

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

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/

val description: String (type after identifier)

●
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?

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}"
}
}
)

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

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
}
}

Black magic
}
0 * any
}
}
Lambda param after
parenthesis
Code generation
(compiler plugin)

Black magic
}
0 * any
}
}
Operator overloading
Reified generics
Extension functions
https://github.com/Koxalen

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

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

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

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

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?

It’s all about LEARNING
and MOTIVATION

Questions?
Andrés Viedma · @andres_viedma

Poniendo Kotlin en producción a palos (Kotlin in production, the hard way)

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