Kotlin DSLs -"mini languge "

This talk introduces and highlights how we could use Kotlin language to build custom DSL’s in android and add some readability of code by enforcing the use of declarative code with minimum boilerplate, as well as look at why Kotlin is particularly good for DSLs with examples.

1. Let’s Express Code “mini language” Kotlin DSL
2. Adit Lal GoPay $6.3B @aditlal We have 18+ products from food tech to fin-tech to hyper local delivery and massage services Ride Sharing 16.5m KM
3. DSL Building blocks of DSL Custom DSL Use cases ?
4. A domain-specific language (DSL) is a computer language specialised to a particular application domain. This is in contrast to a general-purpose language (GPL), which is broadly applicable across domains. DSL
6. Easy to read, Express, Understand DSL
7. Configuration Templates Logic UI ..more DSL
8. Building Blocks Kotlin language features that help build DSL’s
9. Building Blocks Statically typed Syntax <3 DSL IDE + Code completion JVM / Android / JS / Native Kotlin
10. Building Blocks Lambdas with receivers Infix call Invoke Extension functions Kotlin
11. Building Blocks Lambdas with receivers uiLabel.apply { textColor = Color.BLACK backgroundColor = Color.GREEN text = "" }
12. Building Blocks Infix calls infix fun String.concat(other:String) = "$this$other" val a = "a" val b = "b" val c = a concat b
13. Building Blocks Invoke class Family { fun addMember(name: String) {} operator fun invoke(body: Family.() -> Unit) { body() } }
14. Building Blocks Invoke family { addMember("Mom") addMember("Dad") addMember("Kid") } // neat , nested DSL syntax family.addMember(“Aunt") Or
15. Spans Custom spans builders for Android Text
16. Spans
17. Spans val spannable1 = SpannableString("some formatted text") spannable1.setSpan(StyleSpan(Typeface.BOLD), 0, 4, SPAN_EXCLUSIVE_EXCLUSIVE) spannable1.setSpan(StyleSpan(Typeface.ITALIC), 6, 15, SPAN_EXCLUSIVE_EXCLUSIVE) spannable1.setSpan(ForegroundColorSpan(COLOR.RED),17,21, SPAN_EXCLUSIVE_EXCLUSIVE) val spannable2 = SpannableString("nested text") spannable.setSpan(StyleSpan(Typeface.BOLD), 0, 6, SPAN_EXCLUSIVE_EXCLUSIVE) spannable.setSpan(StyleSpan(Typeface.ITALIC), 0, 6, SPAN_EXCLUSIVE_EXCLUSIVE) spannable.setSpan(URLSpan(url), 8, 12, SPAN_EXCLUSIVE_EXCLUSIVE) val spannable3 = SpannableString("no wrapping") spannable.setSpan(StyleSpan(Typeface.BOLD), 0, 42, SPAN_EXCLUSIVE_EXCLUSIVE) spannable.setSpan(SuperscriptSpan(), 4, 12, SPAN_EXCLUSIVE_EXCLUSIVE)
18. fun spannable(func: () -> SpannableString) = func() Spans private fun span(s: CharSequence, o: Any) = (if (s is String) SpannableString(s) else s as? SpannableString ?: SpannableString("")).apply { setSpan(o, 0, length, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE) } operator fun SpannableString.plus(s: SpannableString) = SpannableString(this concat s) operator fun SpannableString.plus(s: String) = SpannableString(this concat s)
19. fun bold(s: CharSequence) = span(s, StyleSpan(android.graphics.Typeface.BOLD)) Spans fun sub(s: CharSequence) = span(s, SubscriptSpan()) // baseline is lowered fun size(size: Float, s: CharSequence) = span(s, RelativeSizeSpan(size)) fun color(color: Int, s: CharSequence) = span(s, ForegroundColorSpan(color)) fun url(url: String, s: CharSequence) = span(s, URLSpan(url)) fun italic(s: CharSequence) = span(s, StyleSpan(android.graphics.Typeface.ITALIC))
20. val spanned = spannable{ bold("some") + italic(" formatted") + color(Color.RED, " text") } Spans val nested = spannable{ bold(italic("nested ")) + url("www.google.com", “text") } val noWrapping = bold("no ") + sub(“wrapping") text_view.text = spanned + nested + noWrapping
21. Intents Simplifying Android Intents
22. var intent = Intent(myActivity, TargetActivity::class) intent.putExtra(“user_id”, user.id) intent.putExtra("some_param_1", user.name) intent.putExtra("some_param_2", false) myActivity.startActivity(intent) Intents
23. myActivity.launchActivity<TargetActivity> { putExtra(INTENT_USER_ID, user.id) putExtra(INTENT_USER_PARAM_1, user.name) putExtra(INTENT_USER_PARAM_2, false) } Intents
24. launchActivity<TargetActivity> { putExtra(INTENT_USER_ID, user.id) addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP) } Intents
25. inline fun <reified T : Any> Activity.launchActivity( requestCode: Int = -1, options: Bundle? = null, noinline init: Intent.() -> Unit = {}) { val intent = newIntent<T>(this) intent.init() if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) { startActivityForResult(intent, requestCode, options) } else { startActivityForResult(intent, requestCode) } } Intents
26. inline fun <reified T : Any> Context.launchActivity( options: Bundle? = null, noinline init: Intent.() -> Unit = {}) { val intent = newIntent<T>(this) intent.init() if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) { startActivity(intent, options) } else { startActivity(intent) } } Intents
27. inline fun <reified T : Any> newIntent(context: Context): Intent = Intent(context, T::class.java) Intents
28. Search fun Use Case
29. toolbar.search { id = R.id.action_search textSubmitted { presenter reduce Search(it) true } onClose { presenter reduce Load() true } } Search
30. class TextSearchBuilder { lateinit var action: (String) -> Boolean } Search class ToolbarSearchBuilder { lateinit var toolbar: Toolbar private var closeAction: (() -> Boolean)? = null private var textChange: TextSearchBuilder? = null private var textSubmitted: TextSearchBuilder? = null }
31. class TextSearchBuilder { lateinit var action: (String) -> Boolean } Search class ToolbarSearchBuilder { lateinit var toolbar: Toolbar private var closeAction: (() -> Boolean)? = null private var textChange: TextSearchBuilder? = null private var textSubmitted: TextSearchBuilder? = null }
32. Search class ToolbarSearchBuilder { fun build(): Toolbar { searchView?.apply { setOnQueryTextListener(...) setOnActionExpandListener(...) } return toolbar } }
33. Search fun textChange(setup: (String) -> Boolean) { textChange = TextSearchBuilder().apply { action = setup } } fun onClose(close: () -> Boolean) { closeAction = close } fun textSubmitted(setup: (String) -> Boolean) { textSubmitted = TextSearchBuilder().apply { action = setup } }
34. Search fun Toolbar.search(setup: ToolbarSearchBuilder.() -> Unit) { with(ToolbarSearchBuilder()) { toolbar = this@search setup() build() } }
35. Broadcast DSL with actions
36. override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) // Unregister when onPause, and register again when it resumes. BroadcastReceiver(this) { onAction("app.SOME_ACTION") { // Do something } onCategory("messages") { // Do something } onDataScheme("file://") { // Do something } } Broadcast
37. typealias Execution = (Intent) -> Unit Broadcast sealed class Instructions { abstract fun matches(intent: Intent): Boolean abstract fun execution(): Execution data class OnAction( val action: String, val execution: Execution ) : Instructions() { override fun matches(intent: Intent): Boolean { return intent.action == action } override fun execution() = execution } }
38. class Builder internal constructor() { private val filter = IntentFilter() private val instructions = mutableListOf<Instructions>() } Broadcast
39. fun onAction(action: String, execution: Execution) { filter.addAction(action) instructions.add(OnAction(action, execution)) } Broadcast fun onDataScheme(scheme: String, execution: Execution) { filter.addDataScheme(scheme) instructions.add(OnDataScheme(scheme, execution)) } fun onCategory(category: String, execution: Execution) { filter.addCategory(category) instructions.add(OnCategory(category, execution)) }
40. internal fun filter() = filter internal fun instructions() = instructions Broadcast
41. class BroadcastReceiver<T>( context: T, constructor: Builder.() -> Unit ) : LifecycleObserver where T : Context, T : LifecycleOwner { ... @OnLifecycleEvent(ON_START) fun start() { appContext.registerReceiver(broadcastReceiver, filter) } @OnLifecycleEvent(ON_DESTROY) fun stop() = appContext.unregisterReceiver(broadcastReceiver) } Broadcast
42. class BroadcastReceiver<T>( context: T, constructor: Builder.() -> Unit ) : LifecycleObserver where T : Context, T : LifecycleOwner { init { val builder = Builder() constructor(builder) filter = builder.filter() instructions = builder.instructions() context.lifecycle.addObserver(this) } } Broadcast
43. override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) // Unregister when onPause, and register again when it resumes. BroadcastReceiver(this) { onAction("app.SOME_ACTION") { // Do something } onCategory("messages") { // Do something } onDataScheme("file://") { // Do something } } Broadcast
44. Tests Make tests more readable
45. • Update preferences to make sure that the user is logged out before the test starts • The user launches the app • The user clicks on “Log In” • We assert that the user sees the logged in text Tests
46. @Test fun logsInWhenUserSelectsLogin() { ... resetLoginInPref() //sets login pref key as false instrumentation.startActivitySync(loginIntent) onView(allOf(withId(R.id.login_button), withText(R.string.login))) .perform(click()) val expectedText = context.getString(R.string.is_logged_in, "true") onView(AllOf.allOf(withId(R.id.label), withText(expectedText))) .perform(ViewActions.click()) } Tests
47. Setup, actions and assertions. Given the user is logged out When the user launches the app When the user clicks “Log In” Then the user sees the logged in text Tests
48. @Test fun logsInWhenUserSelectsLogin() { } Tests given(user).has().loggedOut(); when(user).launches().app(); when(user).selects().login(); then(user).sees().loggedIn();
49. infix fun Any.given(block: () -> Unit) = block.invoke() infix fun Any.whenever(block: () -> Unit) = block.invoke() infix fun Any.then(block: () -> Unit) = block.invoke() Tests
50. object User { infix fun selects(block: SelectsActions.() -> Unit): User { block.invoke(SelectsActions) return this } } Tests
51. object SelectsActions { fun logout() { onView(allOf(withId(R.id.login_button), withText(R.string.logout))) .perform(click()) } fun login() { onView(allOf(withId(R.id.login_button), withText(R.string.login))) .perform(click()) } } Tests
52. @Test fun logsInWhenUserSelectsLogin() { } Tests given { user has { loggedOut() } } whenever { user launches { app() } selects { login() } } then { user sees { loggedIn() } }
53. JSON fun Use Case
54. "person" : { "id": "dd9e889a-a4a9-4930-9f1d-498e44a9cb96", "isActive": true, "picture": "http://placehold.it/32x32", "age": 21, "name": “John Doe”, "gender": "male", "email": “john@mailto.com“, "phone": "+1 (914) 555-2368” } JSON
55. person { Id = "dd9e889a-a4a9-4930-9f1d-498e44a9cb96" isActive = true picture = "http://placehold.it/32x32" age = 21 gender = "male" name { first = "John" last = “Doe" } contact { email = "john@mailto.com" phone = "+1 (914) 555-2368" } JSON
56. Gradle Type safe build logic
57. Gradle
58. Gradle // Groovy implementation ‘com.squareup.okhttp3:okhttp:$okhttpVersion' // Kotlin implementation(“com.squareup.okhttp3:okhttp:${extra["okhttpVersion"]}") // Kotlin, after migrating to buildSrcVersions implementation(Libs.okhttp)
59. Gradle // buildSrc/src/main/kotlin/Versions.kt // Before buildSrcVersions task object Versions { const val com_squareup_okhttp3: String = "3.12.0" } // After buildSrcVersions task object Versions { const val com_squareup_okhttp3: String = "3.12.0" // available: "3.12.1" } // After manual update object Versions { const val com_squareup_okhttp3: String = "3.12.1" } buildSrcVersions: https://goo.gl/8MTFkY ./gradlew buildSrcVersions
60. Gradle // buildSrc/src/main/kotlin/ProjectVersions.kt object ProjectVersions { const val COMPILE_SDK = 28 } // app/build.gradle android { compileSdkVersion(ProjectVersions.COMPILE_SDK) }
61. Gradle // buildSrc/src/main/kotlin/Extensions.kt fun Project.getCiBuildNumber() = if (project.hasProperty("ciBuildNumber") property("ciBuildNumber") else null // app/build.gradle android { defaultConfig { versionCode = getCiBuildNumber() ?: 1 } }
62. Gradle // Groovy buildTypes { debug { ... } release { ... } anotherbuildtype { ... } } // Kotlin buildTypes { getByName("debug") { ... } getByName("release") { ... } create("anotherbuildtype") { ... } }
63. https://superapp.is https://www.gojek.io
64. Adit Lal @aditlal Thats all folks! superapp.is https://adit.dev/tag/dsl/