DSLs in a Kotlin Way - V2

Presentation about Kotlin machinery for DSL grammars. Updated version for a previous talk.

Oferred at the following events

- The Developers Conference, Kotlin Track (July / 2018)

Transcript

1. DSLs IN A
   KOTLIN WAY
   Ubiratan Soares
   July / 2018
   VERSION
   2.0
   

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3. SELECT *
   FROM accounts
   WHERE id=12345
   

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4. SELECT *
   FROM accounts
   WHERE id=12345
   "
   "
   

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5. String sql = SQLiteQueryBuilder
   .select("*")
   .from("accounts")
   .where("id=12345")
   .toString();
   https://github.com/alexfu/SQLiteQueryBuilder
   

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6. 
   
   
   Hey!!"h1>
   Ho!Lets go!!"span>
   !"div>
   !"body>
   !"html>
   

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7. val tree = createHTMLDocument().html {
   body {
   h1 { +"Hey" }
   div {
   +"Ho!" span { +"Lets go!" }
   }
   }
   }
   https://github.com/Kotlin/kotlinx.html
   

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11. Disclaimer : Strategic jump
    

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12. Type Aliases
    Sealed Classes
    Extension Functions
    Extension Properties
    ETC
    

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13. VERSION
    1.0
    

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14. INFIX
    NOTATION
    

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15. class Extractor {
    fun firstLetter(target: String) =
    target[0].toString()
    }
    val k = Extractor().firstLetter("Kotlin")
    

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16. class Extractor {
    infix fun firstLetter(target: String) =
    target[0].toString()
    }
    val k = Extractor() firstLetter "Kotlin"
    
    

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17. object extract {
    infix fun firstLetterOf(target: String)
    = target[0].toString()
    }
    

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18. object extract {
    infix fun firstLetterOf(target: String)
    = target[0].toString()
    }
    val first = extract firstLetterOf "Awesome"
    

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20. object acronymn {
    infix fun from(target: String) = Chainer(
    initials = mutableListOf(),
    seed = target
    )
    }
    

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21. object acronymn {
    infix fun from(target: String) = Chainer(
    initials = mutableListOf(),
    seed = target
    )
    }
    

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22. class Chainer(
    private val initials: MutableList,
    seed: String) {
    init {
    initials += seed.first().toString()
    }
    

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23. class Chainer(…) {
    init {
    initials += seed.first().toString()
    }
    infix fun and(another: String) =
    Chainer(initials, another)
    

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24. class Chainer(…) {
    init {
    initials += seed.first().toString()
    }
    infix fun and(another: String) =
    Chainer(initials, another)
    

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25. sealed class Joiner
    object noPunctuaction : Joiner()
    object dots : Joiner()
    

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26. class Chainer(…) {
    infix fun joinedWith(option: Joiner) =
    initials.reduce { previous, letter !"
    val next = when (option) {
    is noPunctuaction !" letter
    is dots !" "$letter."
    }
    "$previous$next"
    }
    

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27. class Chainer(…) {
    infix fun joinedWith(option: Joiner) =
    initials.reduce { previous, letter !"
    val next = when (option) {
    is noPunctuaction !" letter
    is dots !" "$letter."
    }
    "$previous$next"
    }
    

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28. class Chainer(…) {
    infix fun joinedWith(option: Joiner) =
    initials.reduce { previous, letter !"
    val next = when (option) {
    is noPunctuaction !" letter
    is dots !" "$letter."
    }
    "$previous$next"
    }
    

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29. class Chainer(…) {
    infix fun joinedWith(option: Joiner) =
    initials.reduce { previous, letter !"
    val next = when (option) {
    is noPunctuaction !" letter
    is dots !" "$letter."
    }
    "$previous$next"
    }
    

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30. val dsl = acronymn from
    "Domain" and
    "Specific" and
    "Language" joinedWith
    noPunctuaction //DSL
    

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31. val dsl = acronymn from
    "Domain" and
    "Specific" and
    "Language" joinedWith
    dots //D.S.L
    

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32. OPERATOR
    OVERLOADS
    

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33. val items = mutableListOf(1, 2, 3)
    items += 4
    

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34. val items = mutableListOf(1, 2, 3)
    items += 4
    /#$
    * Adds the specified [element] to this mutable collection.
    %&
    @kotlin.internal.InlineOnly
    public inline operator fun MutableCollection.plusAssign(element: T) {
    this.add(element)
    }
    

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35. typealias IntPair = Pair
    val calendar by lazy {
    Calendar.getInstance()
    }
    

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36. operator fun Date.plus(args: IntPair): Date {
    calendar.time = this
    calendar.add(args.first, args.second)
    return calendar.time
    }
    operator fun Date.minus(args: IntPair): Date {
    calendar.time = this
    calendar.add(args.first, -args.second)
    return calendar.time
    }
    

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37. operator fun Date.plus(args: IntPair): Date {
    calendar.time = this
    calendar.add(args.first, args.second)
    return calendar.time
    }
    operator fun Date.minus(args: IntPair): Date {
    calendar.time = this
    calendar.add(args.first, -args.second)
    return calendar.time
    }
    

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38. fun Int.days() =
    Calendar.DAY_OF_YEAR to this
    fun Int.months() =
    Calendar.MONTH to this
    val atPast = Date() - 2.months()
    val atFuture = Date() + 15.days()
    

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39. val Int.days: IntPair
    get() = Calendar.DAY_OF_YEAR to this
    val Int.months: IntPair
    get() = Calendar.MONTH to this
    

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40. val past = Date() - 2.months
    val future = Date() + 15.days
    
    val Int.days: IntPair
    get() = Calendar.DAY_OF_YEAR to this
    val Int.months: IntPair
    get() = Calendar.MONTH to this
    

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41. A The problem
    like with spannables
    on Android
    

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42. val toSpan = SpannableStringBuilder()
    val start = toSpan.length
    toSpan.append("First Part")
    toSpan.setSpan(
    UnderlineSpan(),
    start,
    toSpan.length,
    Spannable.SPAN_EXCLUSIVE_EXCLUSIVE
    )
    toSpan.setSpan(
    StyleSpan(android.graphics.Typeface.BOLD),
    start,
    toSpan.length,
    Spannable.SPAN_EXCLUSIVE_EXCLUSIVE
    )
    toSpan.append("not bold or underlined")
    
    

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43. operator fun SpannableString.plus(s: String) =
    SpannableString(TextUtils.concat(this, s))
    operator fun SpannableString.plus(s: SpannableString) =
    SpannableString(TextUtils.concat(this, s))
    

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44. fun span(given: CharSequence, span: Any): SpannableString {
    val spannable =
    if (given is String) SpannableString(given)
    else given as? SpannableString ?: throw CannotBeSpanned
    return spannable.apply {
    setSpan(span, 0, length, SPAN_EXCLUSIVE_EXCLUSIVE)
    }
    }
    object CannotBeSpanned : IllegalArgumentException(
    "Cannot apply span. Should be String or SpannableString"
    )
    

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45. // Add more hooks to same span() function
    fun italic(given: CharSequence) =
    span(given, StyleSpan(Typeface.ITALIC))
    fun underline(given: CharSequence) =
    span(given, UnderlineSpan())
    fun bold(given: CharSequence) =
    span(given, StyleSpan(Typeface.BOLD))
    

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46. val spanned =
    "normal" +
    bold("bold") +
    italic("italic")
    label.setText(spanned)
    

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47. LAMBDAS +
    RECEIVERS
    

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48. fun x(lambda: () !" Unit) { lambda() }
    fun y(lambda: () !" Int) = lambda()
    val x: () !" Int = { TODO() }
    val result = x()
    

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49. val add = fun(a: Int, b: Int) = a + b
    fun calculate(func: (Int, Int) !" Int) {
    func.invoke(2,2)
    }
    // Trailling Notation
    calculate { a, b !" a + b }
    // Normal notation
    calculate(add)
    

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50. class Receiver(val data: Int)
    // Kotlin allows us to add an extension function
    // literal to a type. Such lambda acquires the
    // properties of non-static method in the context
    val addOne: Receiver.() !" Int = {
    data + 1
    }
    val two = addOne(Receiver(1))
    val twoAgain = Receiver(1).addOne()
    

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51. fun receive(block: Receiver.() !" Unit) {
    val r = Receiver(data = 1)
    block(r)
    // r.block() is exactly the same
    }
    receive {
    println(data) // 1
    }
    

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53. https://graphql.org/swapi-graphql/
    

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54. val starWars = query {
    allFilms {
    film { title director }
    }
    }
    println(starWars)
    > query { allFilms { film { title director } } }
    

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55. val starWars = query {
    '( TODO
    }
    

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56. val starWars = query {
    '( TODO
    }
    fun query(): String {
    return "query { ${ '( Something here } }"
    }
    

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57. val starWars = query {
    '( TODO
    }
    fun query(setup: AllFilmsBlock.() !" String) =
    "query { ${setup(AllFilmsBlock())} }"
    

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58. val starWars = query {
    '( TODO
    }
    fun query(setup: AllFilmsBlock.() !" String) =
    "query { ${setup(AllFilmsBlock())} }"
    

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59. val starWars = query {
    '( TODO
    }
    fun query(setup: AllFilmsBlock.() !" String) =
    "query { ${setup(AllFilmsBlock())} }"
    

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60. fun query(setup: AllFilmsBlock.() !" String) =
    "query { ${setup(AllFilmsBlock())} }"
    val starWars = query {
    allFilms { // TODO }
    }
    class AllFilmsBlock {
    fun allFilms(setup: FilmBlock.() !" String) =
    "allFilms { ${setup(FilmBlock())} }"
    }
    

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61. fun query(setup: AllFilmsBlock.() !" String) =
    "query { ${setup(AllFilmsBlock())} }"
    val starWars = query {
    allFilms { // TODO }
    }
    class AllFilmsBlock {
    fun allFilms(setup: FilmBlock.() !" String) =
    "allFilms { ${setup(FilmBlock())} }"
    }
    

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62. val starWars = query {
    allFilms {
    film {
    // TODO
    }
    }
    }
    

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63. val starWars = query {
    allFilms { film { } }
    }
    class FilmBlock {
    fun film(setup: FilmFields.() !" String) =
    with(FilmFields()) {
    setup()
    "film { ${fields()} }"
    }
    }
    

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64. val starWars = query {
    allFilms { film { } }
    }
    class FilmBlock {
    fun film(setup: FilmFields.() !" String) =
    with(FilmFields()) {
    setup()
    "film { ${fields()} }"
    }
    }
    

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65. val starWars = query {
    allFilms { film { } }
    }
    class FilmBlock {
    fun film(setup: FilmFields.() !" String) =
    with(FilmFields()) {
    setup()
    "film { ${fields()} }"
    }
    }
    

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66. class FilmFiels {
    private val picked = mutableListOf()
    fun fields() = TODO()
    val title: String
    get() {
    picked.add(TITLE)
    return TITLE
    }
    }
    

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67. class FilmFields {
    val title: String
    get() { … }
    val director: String
    get() { … }
    private companion object {
    const val TITLE = "title"
    const val DIRECTOR = "director"
    }
    }
    

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68. class FilmFields {
    fun fields() =
    picked.distinct().joinToString(separator = " ")
    val title: String
    get() { … }
    val director: String
    get() { … }
    private companion object { … }
    }
    

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69. class FilmFields {
    fun fields() =
    picked.distinct().joinToString(separator = " ")
    val title: String
    get() { … }
    val director: String
    get() { … }
    private companion object { … }
    }
    

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70. val starWars = query {
    allFilms {
    film {
    title
    director
    }
    }
    }
    println(starWars)
    

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72. // Plain old mockWebServer
    val server = MockWebServer()
    val response = MockResponse().apply {
    setResponseCode(503)
    setBody("Ops!")
    }
    server.enqueue(response)
    server.start()
    

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73. class MockResponseBuilder(
    '( Aliases
    var code: Int = 0,
    var response: String? = null) {
    fun mockResponse() = MockResponse().apply {
    setResponseCode(code)
    setBody(response)
    }
    }
    

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74. class QueueBuilder {
    val mocks = mutableListOf()
    fun enqueueMock(setup: MockResponseBuilder.() !" Unit) {
    val builder = MockResponseBuilder()
    builder.setup()
    mocks.add(builder.mockResponse())
    }
    }
    

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75. typealias BuildMock = MockResponseBuilder.() !" Unit
    class QueueBuilder {
    val mocks = mutableListOf()
    fun enqueueMock(setup: BuildMock) =
    MockResponseBuilder().run {
    setup()
    mocks.add(mockResponse())
    }
    }
    

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76. typealias BuildMock = MockResponseBuilder.() !" Unit
    class QueueBuilder {
    val mocks = mutableListOf()
    fun enqueueMock(setup: BuildMock) =
    MockResponseBuilder().run {
    setup()
    mocks.add(mockResponse())
    }
    }
    

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77. typealias BuildQueue = QueueBuilder.() !" Unit
    fun newServer(setup: BuildQueue): MockWebServer =
    with(MockWebServer()) {
    '( ????
    return this
    }
    

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78. typealias BuildQueue = QueueBuilder.() !" Unit
    fun newServer(setup: BuildQueue): MockWebServer =
    with(MockWebServer()) {
    QueueBuilder().run {
    setup()
    mocks.forEach { enqueue(it) }
    }
    return this
    }
    

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79. typealias BuildQueue = QueueBuilder.() !" Unit
    fun newServer(setup: BuildQueue): MockWebServer =
    with(MockWebServer()) {
    QueueBuilder().run {
    setup()
    mocks.forEach { enqueue(it) }
    }
    return this
    }
    

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80. // DSL based
    val server = newServer {
    enqueueMock {
    code = 200
    response = "OK"
    }
    }
    server.start()
    // Plain old mockWebServer
    val server = MockWebServer()
    val response = MockResponse().apply {
    setResponseCode(503)
    setBody("Ops!")
    }
    server.enqueue(response)
    server.start()
    

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82. FINAL

    REMARKS
    

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83. CONCLUSIONS
    • DSLs are fun (with no pun)
    • DSL-building offer great insights over Kotlin features!
    • DSLs should work to improve an existing domain, not replace it
    • Design your own DSLs for fun and profit !
    

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84. https://speakerdeck.com/ubiratansoares
    

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85. UBIRATAN
    SOARES
    Computer Scientist by ICMC/USP
    Software Engineer, curious guy
    Google Expert for Android and Kotlin
    Teacher, speaker, etc, etc
    

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86. THANK YOU
    @ubiratanfsoares
    ubiratansoares.github.io
    https://br.linkedin.com/in/ubiratanfsoares
    

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