DSLs in a Kotlin Way - V2

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

SELECT * FROM accounts WHERE id=12345

SELECT * FROM accounts WHERE id=12345 " "

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

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

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

Disclaimer : Strategic jump

Type Aliases Sealed Classes Extension Functions Extension Properties ETC

VERSION 1.0

INFIX NOTATION

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

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

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

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

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

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

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

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

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

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

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

OPERATOR OVERLOADS

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

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

typealias IntPair = Pair<Int, Int> val calendar by lazy {
Calendar.getInstance() }

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 }

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()

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

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

A The problem like with spannables on Android

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")

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

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" )

// 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))

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

LAMBDAS + RECEIVERS

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

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)

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()

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

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

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

val starWars = query { '( TODO }

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

// 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()

FINAL  REMARKS

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 !

https://speakerdeck.com/ubiratansoares

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

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

DSLs in a Kotlin Way - V2

DSLs in a Kotlin Way - V2

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