Andropower of Kotlin DSL

DSL is a good way to write code declaratively. Kotlin simplifies many things for us and gave the possibility to write our own DSL for APIs. In the talk, you can find out how to write Kotlin DSL and how it can be applied to improve Android APIs.

Transcript

1. Andropower of Kotlin DSL
   

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2. Kirill Rozov
   krl.rozov@gmail.com
   Lead Android Developer@
   

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3. android_broadcast
   News for Android Devs
   

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4. Agenda
   • What is DSL?
   
   • Kotlin DSL
   
   • How to build own DSL
   
   • Where to apply Kotlin DSL
   

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5. A domain-specific language (DSL) is a computer language
   specialised to a particular application domain. DSL is opposite for
   general-purpose language (GPL), which is broadly applicable across
   domains
   wikipedia.org/wiki/Domain-specific_language
   

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6. Examples of DSL Languages
   • SQL
   
   • HTML
   
   • CSS
   
   • Regular expressions
   

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7. DSL positives
   

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8. DSL positives
   +Stricter API for specific domain
   

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9. DSL positives
   +Stricter API for specific domain
   +Better solve special tasks
   

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10. DSL negatives
    

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11. DSL negatives
    — Non-trivial to validate the correct interaction of the DSL with the host
    language at compile time

    Harder to debug the DSL program and to provide IDE code completion
    

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12. DSL negatives
    — Non-trivial to validate the correct interaction of the DSL with the host
    language at compile time

    Harder to debug the DSL program and to provide IDE code completion
    — Can be difficult to combine with a host application in a GPL

    Need to either store program written in DSL in a separate file or embed it in a string literal
    

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13. DSL negatives
    — Non-trivial to validate the correct interaction of the DSL with the host
    language at compile time

    Harder to debug the DSL program and to provide IDE code completion
    — Can be difficult to combine with a host application in a GPL

    Need to either store program written in DSL in a separate file or embed it in a string literal
    — The separate syntax requires separate learning
    

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14. As opposed to external DSLs, which have their own independent
    syntax, internal DSLs are part of programs written in a general-
    purpose language, using exactly the same syntax
    

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15. As opposed to external DSLs, which have their own independent
    syntax, internal DSLs are part of programs written in a general-
    purpose language, using exactly the same syntax
    … and Kotlin has it
    

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16. 
    
    
    This is a title
    
    
    Hello
    world!
    
    
    DSL Sample .html
    

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17. DSL Sample .java
    

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18. HtmlBuilder htmlBuilder = createHtml();
    htmlBuilder.head()
    .title("This is a title");
    htmlBuilder.body()
    .add(p("Hello”))
    .add(p("world!"));
    String html = htmlBuilder.build();
    DSL Sample .java
    

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19. val html = html {
    head {
    title("This is a title")
    }
    body {
    p("Hello")
    p("world!")
    }
    }
    DSL Sample .kt
    

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20. Libraries with Kotlin DSL
    • Kotlin Anko UI DSL

    github.com/Kotlin/anko
    
    • Gradle Kotlin DSL

    github.com/gradle/kotlin-dsl
    
    • kotlinx.html

    github.com/Kotlin/kotlinx.html
    
    • Spek

    spekframework.org
    
    • Kakao

    github.com/agoda-com/Kakao
    

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21. xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    android:id="@+id/name"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />
    android:id="@+id/say_hello"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />
    
    Android Layout XML
    

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22. verticalLayout {
    val name = editText()
    button("Say Hello") {
    onClick { toast("Hello, ${name.text}!") }
    }
    }
    Anko UI
    

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23. apply(plugin = "java-library")
    dependencies {
    "api"("junit:junit:4.12")
    "implementation"("junit:junit:4.12")
    "testImplementation"("junit:junit:4.12")
    }
    configurations {
    "implementation" {
    resolutionStrategy.failOnVersionConflict()
    }
    }
    Gradle Kotlin DSL
    

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24. Kotlin DSL building blocks
    

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25. Kotlin DSL building blocks
    • Extension function

    String.capitalize()
    
    • Operator overloading

    mutableList += “item”
    
    • Infix function call

    1 to “one”
    
    • Lambda outside of parentheses

    reader.use { it.readLine() }
    
    • Lambda with receiver

    StringBuilder.() -> Unit
    

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26. Lambda with receiver
    fun buildString(body: (StringBuilder) -> Unit): String {
    val builder = StringBuilder()
    body(builder)
    return builder.toString()
    }
    

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27. Lambda with receiver
    fun buildString(body: (StringBuilder) -> Unit): String {
    val builder = StringBuilder()
    body(builder)
    return builder.toString()
    }
    buildString {
    it.append("Hello")
    it.append(' ')
    it.append("world")
    }
    

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28. Lambda with receiver
    fun buildString(body: (StringBuilder) -> Unit): String {
    val builder = StringBuilder()
    body(builder)
    return builder.toString()
    }
    buildString {
    it.append("Hello")
    it.append(' ')
    it.append("world")
    }
    it: StringBuilder ->
    

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29. Lambda with receiver
    fun buildString(body: (StringBuilder) -> Unit): String {
    val builder = StringBuilder()
    body(builder)
    return builder.toString()
    }
    

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30. Lambda with receiver
    fun buildString(body: StringBuilder.() -> Unit): String {
    val builder = StringBuilder()
    body(builder)
    return builder.toString()
    }
    

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31. Lambda with receiver
    fun buildString(body: StringBuilder.() -> Unit): String {
    val builder = StringBuilder()
    builder.body()
    return builder.toString()
    }
    

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32. Lambda with receiver
    fun buildString(body: StringBuilder.() -> Unit): String {
    val builder = StringBuilder()
    builder.body()
    return builder.toString()
    }
    

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33. Lambda with receiver
    fun buildString(body: StringBuilder.() -> Unit): String {
    val builder = StringBuilder()
    builder.body()
    return builder.toString()
    }
    

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34. Lambda with receiver
    fun buildString(body: StringBuilder.() -> Unit): String {
    val builder = StringBuilder()
    builder.body()
    return builder.toString()
    }
    

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35. Lambda with receiver
    fun buildString(body: StringBuilder.() -> Unit): String {
    val builder = StringBuilder()
    builder.body()
    return builder.toString()
    }
    

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36. Lambda with receiver
    fun buildString(body: StringBuilder.() -> Unit): String {
    val builder = StringBuilder()
    builder.body()
    return builder.toString()
    }
    

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37. Lambda with receiver
    buildString {
    append("Hello")
    append(' ')
    append("world")
    }
    

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38. Lambda with receiver
    buildString {
    append("Hello")
    append(' ')
    append("world")
    }
    this: StringBuilder
    

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39. with from std library
    inline fun with(receiver: T, block: T.() -> R): R {
    return receiver.block()
    }
    with(StringBuilder()) {
    append("Hello")
    append(' ')
    append("world")
    }
    

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40. with from std library
    with(StringBuilder()) {
    append("Hello")
    append(' ')
    append("world")
    }
    

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41. with from std library
    with(StringBuilder()) {
    append("Hello")
    append(' ')
    append("world")
    }
    new StringBuilder()
    .append("Hello")
    .append(' ')
    .append("world");
    

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42. StrictModeCompat
    github.com/kirich1409/StrictModeCompat
    

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43. StrictMode.ThreadPolicy threadPolicy =
    new StrictModeCompat.ThreadPolicy.Builder()
    .detectResourceMismatches()
    .detectUnbufferedIo()
    .penaltyLog()
    .build();
    StrictMode.VmPolicy vmPolicy = new StrictModeCompat.VmPolicy.Builder()
    .detectFileUriExposure()
    .detectLeakedRegistrationObjects()
    .detectContentUriWithoutPermission()
    .penaltyLog()
    .penaltyFlashScreen()
    .build();
    StrictModeCompat.setPolicies(threadPolicy, vmPolicy);
    Android StrictMode Sample
    

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44. initStrictMode {
    threadPolicy {
    resourceMismatches = true
    unbufferedIo = true
    penalty {
    log = true
    }
    }
    vmPolicy {
    fileUriExposure = true
    leakedRegistrationObjects = true
    contentUriWithoutPermission = true
    penalty {
    log = true
    flashScreen = true
    }
    }
    }
    Android StrictMode Sample
    

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45. fun initStrictMode(
    config: StrictModeConfig.() -> Unit
    ) {
    …
    }
    Android StrictMode Sample
    

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46. fun initStrictMode(
    config: StrictModeConfig.() -> Unit
    ) {
    …
    }
    Android StrictMode Sample
    

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47. fun initStrictMode(
    config: StrictModeConfig.() -> Unit
    ) {
    …
    }
    Android StrictMode Sample
    

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48. class StrictModeConfig {
    var threadPolicyConfig = ThreadPolicyConfig()
    private set
    var vmPolicyConfig = VmPolicyConfig()
    private set
    fun threadPolicy(config: ThreadPolicyConfig.() -> Unit) {
    threadPolicyConfig.apply(config)
    }
    fun vmPolicy(config: VmPolicyConfig.() -> Unit) {
    vmPolicyConfig.apply(config)
    }
    }
    Android StrictMode Sample
    

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49. class ThreadPolicyConfig {
    var customSlowCalls = false
    var diskReads = false
    var diskWrites = false
    var network = false
    var resourceMismatches = false
    var unbufferedIo = false
    var penaltyConfig = PenaltyConfig()
    private set
    fun penalty(config: PenaltyConfig.() -> Unit) {
    penaltyConfig.apply(config)
    }
    }
    Android StrictMode Sample
    

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50. class PenaltyConfig {
    var death = false
    var deathOnNetwork = false
    var dialog = false
    var dropBox = false
    var flashScreen = false
    var log = false
    }
    Android StrictMode Sample
    

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51. fun initStrictMode(
    config: StrictModeConfig.() -> Unit
    ) {
    StrictModeConfig().apply {
    config()
    val threadPolicy =
    buildThreadPolicy(threadPolicyConfig)
    StrictMode.setThreadPolicy(threadPolicy)
    val vmPolicy = buildVmPolicy(vmPolicyConfig)
    StrictMode.setVmPolicy(vmPolicy)
    }
    }
    Android StrictMode Sample
    

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52. fun buildThreadPolicy(
    config: ThreadPolicyConfig
    ): ThreadPolicy {
    val builder = StrictModeCompat.ThreadPolicy.Builder()
    if (config.customSlowCalls) builder.detectCustomSlowCalls()
    if (config.diskReads) builder.detectDiskReads()
    …
    config.penaltyConfig.let {
    if (it.death) builder.penaltyDeath()
    if (it.deathOnNetwork) builder.penaltyDeathOnNetwork()
    …
    }
    return threadPolicyBuilder.build()
    }
    Android StrictMode Sample
    

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53. initStrictMode {
    threadPolicy {
    resourceMismatches = true
    unbufferedIo = true
    penalty {
    log = true
    }
    }
    }
    Android StrictMode Sample
    this: StrictModeConfig
    this: ThreadPolicyConfig
    this: PenaltyConfig
    

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54. initStrictMode {
    threadPolicy {
    resourceMismatches = true
    unbufferedIo = true
    penalty {
    log = true
    threadPolicy {
    …
    }
    }
    }
    }
    Android StrictMode Sample
    this: StrictModeConfig
    this: ThreadPolicyConfig
    this: PenaltyConfig
    

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55. initStrictMode {
    threadPolicy {
    resourceMismatches = true
    unbufferedIo = true
    penalty {
    log = true
    threadPolicy {
    …
    }
    }
    }
    }
    Android StrictMode Sample
    this: StrictModeConfig
    this: ThreadPolicyConfig
    this: PenaltyConfig
    

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56. @DslMarker
    annotation class StrictModeDsl
    Android StrictMode Sample
    

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57. class StrictModeConfig() {
    var threadPolicyConfig = ThreadPolicyConfig()
    private set
    var vmPolicyConfig = VmPolicyConfig()
    private set
    fun threadPolicy(
    config: ThreadPolicyConfig.() -> Unit
    ) {
    threadPolicyConfig.apply(config)
    }
    fun vmPolicy(config: VmPolicyConfig.() -> Unit) {
    vmPolicyConfig.apply(config)
    }
    }
    Android StrictMode Sample
    

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58. @StrictModeDsl
    class StrictModeConfig() {
    var threadPolicyConfig = ThreadPolicyConfig()
    private set
    var vmPolicyConfig = VmPolicyConfig()
    private set
    fun threadPolicy(
    config: @StrictModeDsl ThreadPolicyConfig.() -> Unit
    ) {
    threadPolicyConfig.apply(config)
    }
    fun vmPolicy(config: @StrictModeDsl VmPolicyConfig.() -> Unit) {
    vmPolicyConfig.apply(config)
    }
    }
    Android StrictMode Sample
    

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59. initStrictMode {
    threadPolicy {
    resourceMismatches = true
    unbufferedIo = true
    penalty {
    log = true
    threadPolicy {
    …
    }
    }
    }
    }
    Android StrictMode Sample
    

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60. Where to apply Kotlin DSL ?
    • As replacement of the Builder pattern
    
    • As mediator between different DSL and Kotlin code

    SQL, HTML, etc
    

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61. Ideas to do
    

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62. Ideas to do
    • Android System Notification
    

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63. Ideas to do
    • Android System Notification
    • Android Spannable String

    Android-KTX already have basic implementation's
    

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64. Ideas to do
    • Android System Notification
    • Android Spannable String

    Android-KTX already have basic implementation's
    • Alert Dialogs
    

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65. Thank YOU!!!
    

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