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KOTLIN DSLs Wolfram Rittmeyer

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2 What are DSLs

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3 DSLs ● Easily understandable ● Make the intention obvious ● Are specific to a problem

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4 DSLs ● External DSLs – Use any language to implement it ● Internal DSLs – Uses host language – Uses normal language constructs – Can use language constructs within DSL

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5 Samples

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6 kotlintest should("verify names in map") { //... name should (startWith("test") or endWith("Name")) name shouldBe "testName" ageMap should contain("testName") }

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7 Koin val appModule = applicationContext { val db = SomeDatabase.getInstance(applicationContext) bean { db.entryDao } bean { SomeApi.create(BuildConfig.DEBUG) } bean("MainScheduler") { AndroidSchedulers.mainThread() as Scheduler } factory { AndroidNotifBuilder(applicationContext) as NotificationBuilder } }

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8 Anko constraintLayout { val title = textView { id = R.id.txtTitle textAppearance = R.style.TextAppearance_AppCompat_Large textColor = R.color.titleText } applyConstraintSet { title { connect( TOP to TOP of PARENT_ID margin dip(16), START to START of PARENT_ID margin dip(16) ) } } }

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9 How is it done?

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10 mockK view = mockk(relaxed = true) // ... every { view.setRemoteVehicles(vehicles = capture(params)) } just runs

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11 mockK just runs

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12 mockK

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13 mockK /** * Part of DSL. Answer placeholder for Unit returning functions. */ infix fun MockKStubScope.just(runs: Runs) = answers(ConstantAnswer(Unit))

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14 mockK /** * Part of DSL. Answer placeholder for Unit returning functions.

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15 mockK just(runs)

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16 mockK just runs

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17 Concepts covered so far ● Infix calls

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18 mockK view = mockk(relaxed = true) // ... every { view.setRemoteVehicles(vehicles = capture(params)) } just runs

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19 mockK just runs

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20 mockK runs

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21 mockK /** * Part of DSL. Object to represent phrase "just Runs" */ object Runs typealias runs = Runs

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22 Concepts covered so far ● Infix calls ● Empty object ● Type aliases

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23 kotlintest class CalenderListScreen : ShouldSpec() { init { should("display channelMap in list") { // ... } } }

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24 kotlintest

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25 kotlintest fun should(name: String, test: () -> Unit): TestCase { val testCase = TestCase( suite = current, name = "should $name", test = test, config = defaultTestCaseConfig) current.addTestCase(testCase) return testCase }

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26 kotlintest

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27 kotlintest

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28 kotlintest

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29 Concepts covered so far ● Infix calls ● Empty object ● Type aliases ● Trailing lambdas

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30 kotlintest class CalenderListScreen : ShouldSpec() { init { should("display channelMap in list") { // ... } } }

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31 kotlintest class CalenderListScreen : StringSpec() { init { "should display channelMap in list" { // ... } } }

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32 kotlintest

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33 kotlintest operator fun String.invoke(test: () -> Unit): TestCase { val tc = TestCase(suite = rootTestSuite, name = this, test = test, config = defaultTestCaseConfig) rootTestSuite.addTestCase(tc) return tc }

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34 kotlintest

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35 Concepts covered so far ● Infix calls ● Empty object ● Type aliases ● Trailing lambdas ● Extension functions ● Conventions

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36 kotlinx.html val html = buildString { appendHTML().html { body { div { +"Some text inside the div" } } } }

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37 kotlinx.html +"Some text inside the div"

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38 kotlinx.html @kotlinx.html.HtmlTagMarker public interface Tag { // ... public open operator fun kotlin.String.unaryPlus(): kotlin.Unit { /* ... */ } // ... }

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39 kotlinx.html

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40 Concepts covered so far ● Infix calls ● Empty object ● Type aliases ● Trailing lambdas ● Conventions ● Extension functions ● Operator overloading

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41 Koin val appModule = applicationContext { val db = SomeDatabase.getInstance(applicationContext) bean { db.entryDao } bean { SomeApi.create(BuildConfig.DEBUG) } bean("MainScheduler") { AndroidSchedulers.mainThread() as Scheduler } factory { AndroidNotifBuilder(applicationContext) as NotificationBuilder } }

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42 Koin

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43 Koin fun applicationContext(init: Context.() -> Unit): Module = { Context(Scope.ROOT, StandAloneContext.koinContext as KoinContext).apply(init) }

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44 Koin

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45 Koin fun applicationContext(init: Context.() -> Unit): Module = { Context(Scope.ROOT, StandAloneContext.koinContext as KoinContext).apply(init) }

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46 Koin fun applicationContext(init: Context.() -> Unit): Module = { val ctx = Context(Scope.ROOT, StandAloneContext.koinContext as KoinContext) ctx.init() }

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47 Lambda vs. Lambda with receivers "heyho".also { str -> println(str) }

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48 Lambda vs. Lambda with receivers "heyho".also { println(it) }

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49 Lambda vs. Lambda with receivers "heyho".also { println(it) } "heyho".apply { println(this) }

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50 Lambda vs. Lambda with receivers // slightly simplified public inline fun T.also(block: (T) -> Unit): T { block(this) return this } // slightly simplified public inline fun T.apply(block: T.() -> Unit): T { block() return this }

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51 Lambda vs. Lambda with receivers

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52 Lambda with receivers in DSLs

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53 Lambda with receivers in DSLs fun applicationContext(init: Context.() -> Unit): Module = { val ctx = Context(Scope.ROOT, StandAloneContext.koinContext as KoinContext) ctx.init() }

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54 Concepts covered so far ● Infix calls ● Empty object ● Type aliases ● Trailing lambdas ● Conventions ● Extension functions ● Operator overloading ● Lambda with Receivers

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55 Anko constraintLayout { val title = textView { id = R.id.txtTitle textAppearance = R.style.TextAppearance_AppCompat_Large textColor = R.color.titleText } applyConstraintSet { title { connect( TOP to TOP of PARENT_ID margin dip(16), START to START of PARENT_ID margin dip(16) ) } } }

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56 Anko

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57 Anko inline fun ViewManager.textView( init: (@AnkoViewDslMarker android.widget.TextView).() -> Unit) : android.widget.TextView {

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58 Anko

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59 Anko @DslMarker @Target(AnnotationTarget.TYPE) annotation class AnkoViewDslMarker

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60 Concepts ● Infix calls ● Empty object ● Type aliases ● Trailing lambdas ● Conventions ● Extension functions ● Operator overloading ● Lambda with Receivers ● Scope limiting

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61 Summary

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62 Concepts covered so far ● Infix calls ● Empty object ● Type aliases ● Trailing lambdas ● Conventions ● Extension functions ● Operator overloading ● Lambda with Receivers ● Scope limiting

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63 Designing DSLs ● Consider deviating from naming conventions ● As per usual: Don’t go overboard ● An interesting discussion of approaches: https:/ /github.com/zsmb13/VillageDSL

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64 Libs

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65 General libs ● DI / Service Locating: – Koin – Kodein ● Testing – MockK – Spek – kotlintest

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66 Android specific libs ● Anko ● Konduit

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67 Libs ● Spring Router Config ● Spring Bean Config ● Gradle Kotlin DSL ● kotlinx.HTML ● Exposed

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Q&A www.wolfram-rittmeyer.de twitter.com/RittmeyerW www.grokkingandroid.com