Kotlin DSL in under an hour, DevoxxUK 2023

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Kotlin DSL in under an hour @antonarhipov

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Why Kotlin?

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Null-safety Coroutines Multiplatform Syntax Why Kotlin?

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Null-safety Coroutines Multiplatform Syntax Why Kotlin?

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Null-safety Coroutines Multiplatform Syntax Why Kotlin?

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Null-safety Coroutines Multiplatform Syntax Why Kotlin?

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Null-safety Coroutines Multiplatform Syntax Why Kotlin? DSL

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“Domain-speci fi c”, i.e.

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tailored for a speci fi c task “Domain-speci fi c”, i.e.

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External

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External VS Internal

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External VS Internal

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External VS Internal

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External VS Internal

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External VS Internal

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Internal

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Exposed https://github.com/JetBrains/Exposed object Cities : Table() { val id = integer("id").autoIncrement().primaryKey() // Column val name = varchar("name", 50) // Column }

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Exposed https://github.com/JetBrains/Exposed object Cities : Table() { val id = integer("id").autoIncrement().primaryKey() // Column val name = varchar("name", 50) // Column } transaction { create (Cities) val tallinnId = Cities.insert { it[name] = "Tallinn" } get Cities.id for (city in Cities.selectAll()) { println("${city[Cities.id]}: ${city[Cities.name]}") } }

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Kotlin DSL in TeamCity project { vcsRoot(ApplicationVcs) buildType { id("Application") name = "Application" vcs { root(ApplicationVcs) } artifactRules = "target/*jar" steps { maven { goals = "clean package" } } triggers { vcs {} } dependencies { snapshot(Library) {}

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fun main() { embeddedServer(Netty, port = 8080, host = “0.0.0.0", module = Application :: module).start(wait = true) } fun Application.main() { install(DefaultHeaders) install(CallLogging) routing { get("/") { call.respondHtml { head { title { +"Ktor App" } } body { p { +"Hello from Ktor!" } Ktor + kotlinx.html

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They all look similar!

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foo { bar { baz = "Hello!" qux = quux { corge = "Blah" } } }

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foo { bar { baz = "Hello!" qux = quux { corge = "Blah" } } }

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foo { bar { baz = "Hello!" qux = quux { corge = "Blah" } } }

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foo { bar { baz = "Hello!" qux = quux { corge = "Blah" } } }

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foo { bar(grault = 1) { baz = "Hello!" qux = quux { corge = "Blah" } } }

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foo { bar(grault = 1) { baz = "Hello!" qux = quux { corge = Blah() } } }

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foo { bar(grault = 1) { baz = "Hello!" qux = quux { corge = Blah() } } }

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Let’s write some code! https://github.com/antonarhipov/kotlin-dsl-examples

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Let’s write some code! https://github.com/antonarhipov/kotlin-dsl-examples

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Type-safe builders https://kotlinlang.org/docs/reference/type-safe-builders.html

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final ClientBuilder builder = new ClientBuilder(); builder.setFirstName("Anton"); builder.setLastName("Arhipov"); final TwitterBuilder twitterBuilder = new TwitterBuilder(); twitterBuilder.setHandle("@antonarhipov"); builder.setTwitter(twitterBuilder.build()); final CompanyBuilder companyBuilder = new CompanyBuilder(); companyBuilder.setName("JetBrains"); companyBuilder.setCity("Tallinn"); builder.setCompany(companyBuilder.build()); final Client client = builder.build(); System.out.println("Created client is: " + client); val client = createClient { firstName = "Anton" lastName = "Arhipov" twitter { handle = "@antonarhipov" } company { name = "JetBrains" city = "Tallinn" } } println("Created client is: " + client.consoleString)

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//extension property val Client.consoleString: String get() = "${twitter.handle} ${company.name}" //extension method fun Client.toConsoleString(): String { return "${twitter.handle} ${company.name}" }

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fun createClient(c: ClientBuilder.() -> Unit): Client { val builder = ClientBuilder() c(builder) return builder.build() } fun ClientBuilder.company(t: CompanyBuilder.() -> Unit) { company = CompanyBuilder().apply(t).build() } fun ClientBuilder.twitter(t: CompanyBuilder.() -> Unit) { twitter = TwitterBuilder().apply(t).build() } Lambda with receiver Extension functions

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In fi x notation https://kotlinlang.org/docs/reference/functions.html

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dateTime = LocalDateTime.of(2018, Month.DECEMBER, 11, 0, 0) dateTime = 11 December 2018 at (14 hh 0) infix fun Int.December(n: Int) : LocalDate { return LocalDate.of(n, Month.DECEMBER, this) } infix fun LocalDate.at(n: Pair): LocalDateTime { return this.atTime(n.first, n.second) } infix fun Int.hh(n: Int): Pair { return Pair(this, n) }

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Context Receivers KEEP-259 Experimental

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context(DateContext) @DateDsl infix fun Int.March(n: Int): LD = LD.of(n, Month.MARCH, this) class DateContext Context object Context requirement

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context(DateContext) @DateDsl infix fun Int.March(n: Int): LD = LD.of(n, Month.MARCH, this) class DateContext fun client(block: context(DateContext) ClientBuilder.() - > Unit): Client { val builder = ClientBuilder() with(DateContext()) { block(builder) } return builder.build() } Context object Context requirement Context requirement Context scope

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context(DateContext) @DateDsl infix fun Int.March(n: Int): LD = LD.of(n, Month.MARCH, this) class DateContext val client = client { // .. . dob = 24 March 2000 } 24 March 2000 fun client(block: context(DateContext) ClientBuilder.() - > Unit): Client { val builder = ClientBuilder() with(DateContext()) { block(builder) } return builder.build() } Context object Context requirement Context requirement Context scope The function is available in the context scope The function is not available, missing DateContext

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T.() -> Unit

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kotlin { youtube = "youtube.com/kotlin" slack = "slack.kotl.in" } me { name = "Anton Arhipov" twitter = "@antonarhipov" slides = speakerdeck.com/antonarhipov code = github.com/antonarhipov }