GeekOut_2019_-_Building_DSLs_in_Kotlin.pdf

As Kotlin programming language is getting more popular, the creators of the libraries are starting to provide Kotlin API for their frameworks. The number of libraries that provide a nice little DSL grows constantly. The session introduces you to some of those libraries and explains, how Kotlin makes creating the DSL so simple. Lambdas, extension methods, lambdas with the receiver, and other syntactic sugar make it easy to implement DSL in Kotlin. In a live coding demo, we will create a simple DSL for the existing Java classes that could be used from a Kotlin code.

Transcript

1. Building DSLs in Kotlin @antonarhipov
2. Domain-specific, i.e.
3. tailored for the specific task Domain-specific, i.e.
4. External
5. External VS Internal
6. External VS Internal
7. External VS Internal
8. External VS Internal
9. External VS Internal
10. Internal
11. createHTML().html { head { +"Hello!" } body { ul { p { +"This is my awesome text!" } } } } kotlinx.html https://github.com/Kotlin/kotlinx.html
12. Anko https://github.com/Kotlin/anko verticalLayout { padding = dip(30) val name = editText { hint = "Name" textSize = 24f } val pwd = editText { hint = "Password" textSize = 24f } button("Login") { textSize = 26f onClick { toast("Hello, ${name.text}!") } }
13. Gradle Kotlin DSL https://github.com/gradle/kotlin-dsl plugins { java kotlin("jvm") version "1.2.70" } group = "org.arhan" version = "1.0-SNAPSHOT" repositories { maven { setUrl("http://dl.bintray.com/kotlin/kotlin-eap") } jcenter() } dependencies { val kotlinx_html_version = "0.6.11" compile(kotlin("stdlib-jdk8")) compile("org.jetbrains.kotlinx:kotlinx-html-jvm:${kotlinx_html_version}") testCompile("junit", "junit", "4.12")
14. Exposed https://github.com/JetBrains/Exposed object Cities : Table() { val id = integer("id").autoIncrement().primaryKey() // Column<Int> val name = varchar("name", 50) // Column<String> } 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]}") } }
15. https://github.com/nfrankel/kaadin Kaadin theme = "valo" verticalLayout(margin = true, spacing = true) { tabSheet { tab("Interactions") { accordion { tab("Button", HAND_O_RIGHT) { horizontalLayout(true, true) { button() button("Label") button("Label", HAND_O_RIGHT) button("Click me", onClick = { show("Clicked") }) button("Click me", HAND_O_RIGHT, { show("Clicked") }) } }
16. k8s-kotlin-dsl https://github.com/fkorotkov/k8s-kotlin-dsl val client = DefaultKubernetesClient().inNamespace("default") client.extensions().ingresses().createOrReplace( newIngress { metadata { name = "example-ingress" } spec { backend { serviceName = "example-service" servicePort = IntOrString(8080) } } } )
17. 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) {}
18. fun main(args: Array<String>) { embeddedServer(Jetty, commandLineEnvironment(args)).start(wait = true) } fun Application.main() { install(DefaultHeaders) install(CallLogging) routing { get("/") { call.respondHtml { head { title { +"Ktor App" } } body { p { +"Hello from Ktor!" } } Ktor
19. fun main(args: Array<String>) { embeddedServer(Jetty, commandLineEnvironment(args)).start(wait = true) } fun Application.main() { install(DefaultHeaders) install(CallLogging) routing { get("/") { call.respondHtml { head { title { +"Ktor App" } } body { p { +"Hello from Ktor!" } } Ktor
20. fun main(args: Array<String>) { embeddedServer(Jetty, commandLineEnvironment(args)).start(wait = true) } fun Application.main() { install(DefaultHeaders) install(CallLogging) routing { get("/") { call.respondHtml { head { title { +"Ktor App" } } body { p { +"Hello from Ktor!" } } Ktor
21. They all look similar!
22. foo { bar { baz = "Hello!" qux = quux { corge = "Blah" } } }
23. foo { bar { baz = "Hello!" qux = quux { corge = "Blah" } } }
24. foo { bar { baz = "Hello!" qux = quux { corge = "Blah" } } }
25. foo { bar { baz = "Hello!" qux = quux { corge = "Blah" } } }
26. foo { bar(grault = 1) { baz = "Hello!" qux = quux { corge = "Blah" } } }
27. foo { bar(grault = 1) { baz = "Hello!" qux = quux { corge = Blah() } } }
28. foo { bar(grault = 1) { baz = "Hello!" qux = quux { corge = Blah() } } }
29. foo { bar(grault = 1) { baz = "Hello!" qux = quux { corge = Blah() } } }
30. Let’s write some code! https://github.com/antonarhipov/kotlin-dsl-examples
31. Let’s write some code! https://github.com/antonarhipov/kotlin-dsl-examples
32. Type-safe builders https://kotlinlang.org/docs/reference/type-safe-builders.html
33. 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)
34. //extension property val Client.consoleString: String get() = "${twitter.handle} ${company.name}" //extension method fun Client.toConsoleString(): String { return "${twitter.handle} ${company.name}" }
35. 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 methods
36. twitter { handle = "@antonarhipov" company { name = "JetBrains" city = "Tallinn" } } @DslMarker annotation class ClientDsl @ClientDsl class CompanyBuilderDsl : CompanyBuilder() @ClientDsl class TwitterBuilderDsl : TwitterBuilder() twitter { handle = "@antonarhipov" company { name = "JetBrains" city = "Tallinn" } } Scope control
37. Infix notation https://kotlinlang.org/docs/reference/functions.html
38. 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<Int, Int>): LocalDateTime { return this.atTime(n.first, n.second) } infix fun Int.hh(n: Int): Pair<Int, Int> { return Pair(this, n) }
39. T.() -> Unit
40. me { name = "Anton Arhipov" twitter = "@antonarhipov" } books { courses { Kotlin { Try = "try.kotlinlang.org" Slack = "slack.kotl.in" }