Kotlin: MAX PAYNE (Voxxed Days Minsk, May 2018)

Kotlin gives us a lot of neat features and just general developer satisfaction, but little is known about its hidden costs and pain it causes. This talk is a almost a 3 year combination of small (and no so small) issues we encountered when developing a full-Kotlin application started from the scratch. Bugs, features, performance, testing — it’s all there with our answers, conclusions and advises.

Presented at Voxxed Days Minsk conference on May 26, 2018.

Transcript

1. Kotlin: MAX PAYNE
   Artur Dryomov, Juno Lab
   @arturdryomov
   

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3. Juno Kotlin
   Kotlin Juno
   

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4. Juno Rider
   3 years
   100 % Kotlin
   Kotlin EAP in production
   1.1-EAP
   — 6 months
   1.2-EAP
   — 3 months
   99.9 % crash‑free
   2 week sprints
   4 developers, 1 QA
   

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5. Juno Rider
   cloc main/kotlin
   — 56 K
   cloc test/kotlin
   — 49 K
   cloc androidTest/kotlin
   — 17 K
   

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6. Style
   

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7. Java Tools
   Nope
   

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8. Specifications
   Java AST (Abstract Syntax Tree)
   PSI (Program Structure Interface)
   UAST (Universal AST)
   

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9. Checkstyle
   Checkstyle works only with AST as we depend on ANTLR and Java
   grammar.
   https://github.com/checkstyle/checkstyle/issues/4369
   

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10. Kotlin Tools
    IntelliJ IDEA
    detekt
    + ktlint
    android/lint
    kotlinc --force
    tasks.withType {
    kotlinOptions {
    allWarningsAsErrors = true
    }
    }
    

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11. Infinity War
    val gameBuilder = StringBuilder()
    gameBuilder.append("tic")
    gameBuilder.append("tac")
    gameBuilder.append("toe")
    val game = gameBuilder.toString()
    

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12. Infinity War
    val game = StringBuilder().also {
    it.append("tic")
    it.append("tac")
    it.append("toe")
    }
    .toString()
    

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13. Infinity War
    val game = StringBuilder().let {
    it.append("tic")
    it.append("tac")
    it.append("toe")
    it.toString()
    }
    

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14. Infinity War
    val game = StringBuilder().apply {
    append("tic")
    append("tac")
    append("toe")
    }
    .toString()
    

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15. Infinity War
    val game = StringBuilder().run {
    append("tic")
    append("tac")
    append("toe")
    toString()
    }
    

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16. Infinity War
    val game = with(StringBuilder()) {
    append("tic")
    append("tac")
    append("toe")
    toString()
    }
    

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17. Infinity War
    ?
    CODE_STYLE.md
    

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18. Weird Parts
    

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19. Destructuring
    val (first, second) = Pair(1, 2)
    val (first, second, third) = Triple(1, 2, 3)
    listOf(1 to "one", 2 to "two").map { (number, text) ->
    println("number is $number, text is $text")
    }
    

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20. Destructuring
    data class Person(val firstName: String, val lastName: String)
    val (firstName, lastName) = Person("f", "l")
    data class Person(val lastName: String, val firstName: String)
    val (firstName, lastName) = Person("f", "l") // It works!
    

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21. Destructuring
    data class Person(val firstName: String, val lastName: String)
    {
    operator fun component1() = firstName
    operator fun component2() = lastName
    }
    

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22. Destructuring
    Pair
    , Triple
    data class
    

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23. null
    safety?
    Observable.just(null)
    public static Observable just(T item) {
    ObjectHelper.requireNonNull(item, "The item is null");
    ...
    

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24. null
    safety!!
    @Nullable
    + @NonNull
    

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25. null
    safety!!
    Docs.
    Annotations.
    Abstractions.
    

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26. RxJava 2
    val o: Observable = Observable.just(null)
    // Runtime: NullPointerException
    public static Observable just(T item) {
    ObjectHelper.requireNonNull(item, "The item is null");
    ...
    

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27. Optional
    Swift: ?
    , nil enum Optional
    Kotlin: ?
    , null null
    

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28. Koptional
    https://github.com/gojuno/koptional
    val some = Some(value)
    val none = None
    val optional = nullableValue.toOptional()
    val nullable = o.toNullable()
    

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29. Mockito
    interface Api {
    fun call(id: String)
    }
    class Service(private val api: Api) {
    fun call() = api.call(generateId())
    }
    @Test fun test() {
    val api = Mockito.mock()
    Service(api).call()
    verify(api).call(Mockito.any())
    }
    // Runtime: NullPointerException
    

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30. Mockito
    class Mockito {
    public static T any() {
    return null;
    }
    }
    

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31. Mockito
    fun anything(): T = Mockito.any()
    @Test fun test() {
    val api = Mockito.mock()
    Service(api).call()
    verify(api).call(anything())
    }
    

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32. Mockito
    fun eq(value: T): T = Mockito.eq(obj)
    fun anything(): T = Mockito.any()
    fun whenever(call: T) = Mockito.`when`(call)
    

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33. Gson
    data class Model {
    @SerializedName("model_field")
    val field: String
    }
    val model = Gson().fromJson("{}", Model::javaClass)
    // Runtime: OK
    model.field.toString()
    // Runtime: NullPointerException
    

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34. Gson
    Java Reflection
    

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35. Gson
    data class Model {
    @SerializedName("model_field")
    val field: String
    } : Validatable {
    override fun validate() {
    if (field == null) throw ParseException()
    }
    }
    

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36. Gson
    Moshi vs. Jackson
    Kotlin Reflection (2.5 MiB)
    

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37. null
    safety!!
    Kotlin: The Problem with null
    https://arturdryomov.online/posts/kotlin‑the‑problem‑with‑null/
    

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38. Optimizations
    

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39. inline
    private fun createId(): Int = 42
    vs.
    @Suppress("nothing_to_inline")
    private inline fun createId(): Int = 42
    

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40. inline
    https://youtrack.jetbrains.com/issue/KT‑16769
    Revisit compiler and IDE warning about inline functions
    

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41. const
    companion object {
    private val NUMBER = 42
    }
    public static final class Companion {
    private final int NUMBER = 42;
    private final int getNUMBER() {
    return NUMBER;
    }
    }
    

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42. const
    companion object {
    private const val NUMBER = 42
    }
    public static final class Companion {
    private static final int NUMBER = 42;
    }
    

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43. const
    Primitives + String
    kotlinc
    ?
    

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44. Tools Kotlin Show Kotlin Bytecode
    

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45. Tooling
    

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46. Bugs
    fun multiply(double: Double) = double * double
    1.1.3
    org.jetbrains.kotlin.kapt3.diagnostic.KaptError
    Error while annotation processing
    

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47. Bugs
    https://youtrack.jetbrains.com/issue/KT‑18377
    Syntax error while generating kapt stubs
    

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48. Bugs
    Are a thing!
    

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49. Assemble
    javac
    kotlinc
    kapt
    

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50. kapt
    Kotlin Annotation Processing Tool
    Breaks incremental compilation.
    Throws errors.
    *_MemberInjector.java: error: package does not exist
    

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51. kapt
    A Dagger to Remember
    https://arturdryomov.online/posts/a‑dagger‑to‑remember/
    

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52. Assemble
    — i5-5257U @ 2.70GHz
    — i7-6700K @ 4.00GHz
    

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53. Mainframer
    https://github.com/gojuno/mainframer
    $ rsync laptop mainframe
    $ make
    $ rsync mainframe laptop
    

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54. Mainframer
    $ ./gradlew assembleDebug
    4 minutes 10 seconds
    $ mainframer ./gradlew assembleDebug
    1 minute 10 seconds
    

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55. Assemble
    Remove everything possible.
    Gradle build cache.
    Mainframer.
    

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56. Gradle Kotlin DSL
    

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57. Kotlin versions
    Gradle 4.2 — 1.1.4‑3
    Project — 1.2.0‑beta‑31
    Runtime files in the classpath should have the same version.
    These files were found in the classpath:
    .../dists/.../kotlin-stdlib-1.1.4-3.jar (version 1.1)
    .../caches/.../kotlin-stdlib-1.2.0-beta-31.jar (version 1.2)
    

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58. Kotlin versions
    https://github.com/gradle/kotlin‑dsl/issues/519
    

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59. Groovy
    unitTests.all {
    maxParallelForks = 2
    }
    unitTests.all(KotlinClosure1({
    apply {
    maxParallelForks = 2
    }
    }, this))
    

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60. Groovy
    import groovy.lang.Closure;
    public void unitTests(Closure closure)
    https://issuetracker.google.com/issues/78547461
    

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61. Groovy
    2012: groovy.lang.Closure
    2017: org.gradle.api.Action
    

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62. Groovy
    Promote DSL‑agnostic API
    

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63. Gradle Kotlin DSL
    IDE
    Dynamic Groovy
    Workflow
    Alpha!
    

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64. Spek
    

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65. JUnit
    class SystemTest {
    lateinit var system: System
    @BeforeEach fun create() {
    system = System()
    }
    @BeforeEach fun start() {
    system.boot()
    }
    @Test fun `has boot status`() {
    assertThat(system.status()).isEqualTo(BOOTED)
    }
    @Test fun `has positive uptime`() {
    assertThat(system.uptime()).isNotZero()
    }
    }
    

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66. Spek
    class SystemSpec : Spek({
    val system by memoized { System() }
    context("boot") {
    beforeEachTest {
    system.boot()
    }
    it("has boot status") {
    assertThat(system.status()).isEqualTo(BOOTED)
    }
    it("has positive uptime") {
    assertThat(system.uptime()).isNotZero()
    }
    }
    })
    

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67. Versions
    1.0.89
    : DescribeBody Dsl
    1.1.0-beta3
    : Dsl SpecBody
    1.0
    , 1.1.19
    : do not exist.
    JUnit 4 5
    

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68. memoized
    before and after
    class JustSpec : Spek({
    val system by memoized { System() }
    beforeEachTest {
    println("before $system") // system_before
    }
    afterEachTest {
    println("after $system") // system_after
    }
    })
    // system_before != system_after
    

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69. memoized
    before and after
    https://github.com/JetBrains/spek/issues/213
    Memoized value is not the same before and after test
    

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70. JUnit
    JUnit 5!
    Android Studio
    JUnit 4?
    @RunWith(JUnitPlatform::class)
    fon
    , fit
    Spek IJ plugin.
    JUnit 4
    Fun
    

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71. Spek
    jetbrains/spek spekframework/spek
    Compatibility
    Docs
    Bugs
    100 K tests
    2.0
    

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72. Spek
    Spectrum, KotlinTest
    

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73. Conclusion
    

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74. https://youtrack.jetbrains.com/issues/KT
    

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75. ...
    Kotlin is a thin layer on top of Java, and so it perpetuates through a lot of
    the Javaisms in its model.
    ...
    Chris Lattner (Swift, LLVM, Clang)
    

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76. Java — Executive Committee
    Oracle, Red Hat, Intel, IBM, Eclipse, Twitter, JetBrains...
    24 members
    Kotlin — Language Committee
    JetBrains, Google
    3 members
    

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78. Conclusion
    JVM
    Tooling
    Language
    

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