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

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SELECT * FROM accounts WHERE id=12345

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SELECT * FROM accounts WHERE id=12345 " "

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

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

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

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Disclaimer : Strategic jump

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Type Aliases Sealed Classes Extension Functions Extension Properties ETC

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VERSION 1.0

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INFIX NOTATION

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

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

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

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

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

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

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

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

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

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

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

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

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OPERATOR OVERLOADS

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

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

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

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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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A The problem like with spannables on Android

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

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LAMBDAS + RECEIVERS

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

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

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

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val starWars = query { '( TODO }

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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// 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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FINAL
 REMARKS

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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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https://speakerdeck.com/ubiratansoares

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