Scala vs Kotlin

Talk by Javi Pacheco and Antonio Leiva comparing both languages when developing Android Apps.

Transcript

1. SCALA VS KOTLIN Javi Pacheco @javielinux Antonio Leiva @lime_cl
2. Introduction
3. • JVM based • Functional Language & OOP • Immutability emphasis • Purity & Effects • High-order functions • Flexible syntax, create constructs, infix support Scala is LOVE
4. Who’s using Scala?
5. 47 Degrees Projects Scala Days Scala API Demos Translate Bubble
6. Introduction
7. • JVM based • Object-oriented functional language • Created by JetBrains (IntelliJ, Android Studio) • Simple,lightweight, interoperable
8. • Compiled to Java bytecode • Open source • Kotlin 1.0 Beta 3
9. Who’s using Kotlin?
10. Who’s using Kotlin? BusRadar Omni Reedy Wizbii
11. Hello World!
12. 1. Install plugin
13. 1. Install plugin 2. Create a Kotlin class
14. 1. Install plugin 2. Create a Kotlin class 3. Use “Configure Kotlin in Project”
16. 1. Download SBT and install it Installation
17. 1. Download SBT and install it 2. Install Scala Plugin in IntelliJ Installation
18. 1. Download SBT and install it 2. Install Scala Plugin in IntelliJ 3. Configure your project > sbt Installation
19. Null handling
20. val maybeArtist: Option[Artist] = getArtist()
 maybeArtist map { artist => artist.print() } Some(artist) None artist.print() Nothing Option Monad
21. val artist: Artist = maybeArtist getOrElse(defaultArtist) val maybeArtist: Option[Artist] = Option(getArtist()) Providing a Default Value Java Integration
22. var artist: Artist? = null
 artist.print() var artist: Artist? = null
 artist?.print() Won’t compile Won’t do anything if (artist != null) {
 artist.print()
 } Smart cast var artist: Artist? = null
 artist!!.print() It crashes!
23. UI and Animations
24. verticalLayout {
 val name = editText()
 button("Say Hello") {
 onClick { toast("Hello, ${name.text}!") }
 }
 } Anko
25. Kotlin Android Extensions Import synthetic properties: import kotlinx.android.synthetic.activity_main.* Just use them: override fun onCreate(savedInstanceState: Bundle?) {
 super<BaseActivity>.onCreate(savedInstanceState) setContentView(R.id.main)
 } recycler.layoutManager = GridLayoutManager(this, 2)
 recycler.adapter = ContactsAdapter(contacts)

26. • DSL focused to GUI • Intensive use of Macros • Brings the Functional Programming on Ui editText <~ text("foo") <~~ fadeIn <~ enable Macroid library https://github.com/47deg/functional-views-android
27. Background tasks
28. asyncArtist map { artist => artist.print() } Future Monad val asyncArtist: Future[Artist] = getAsyncArtist val asyncFilm: Future[Film] = getAsyncLastFilm(“Barroso”)
29. For Comprehensions val asyncFilm = for { artist <- getAsyncArtist film <- getAsyncLastFilm(artist.name) } yield (film) asyncFilm map (film => film.print())
30. Anko async {
 val contacts = GetContactsCommand().execute(ctx)
 uiThread {
 recycler.adapter = ContactsAdapter(contacts)
 }
 }
31. Kovenant (promises) async {
 //some (long running) operation, or just:
 1 + 1
 } then {
 i -> "result: $i"
 } successUi {
 msg -> println(msg)
 }
32. Data persistence
33. var myPref: Long by Preference(this, "name", 0) Property delegation val prefValue = myPref
 myPref = 20
34. Anko ManagedSQLiteOpenHelper dbHelper.use {
 select("TABLE_NAME").where("_id = {id}", "id" to 20)
 } db.createTable("TABLE_NAME", true,
 "_id" to INTEGER + PRIMARY_KEY,
 "name" to TEXT) parseList / parseOpt / classParser…
35. slick -> http://slick.typesafe.com/ doobie -> https://github.com/tpolecat/doobie Pure functional JDBC layer for Scala mvessel -> https://github.com/47deg/mvessel JDBC driver written in Scala The main goal is to allow the use of ORMs in Android
36. val xa = DriverManagerTransactor[IO]( "org.postgresql.Driver", "jdbc:postgresql:world", "postgres", "" ) case class Country(code: String, name: String, population: Long) def find(n: String): ConnectionIO[Option[Country]] = sql"select code, name from country where name = $n”.query[Country].option find("France").transact(xa).unsafePerformIO Some(Country(FRA, France)) Doobie Sample
37. Testing
38. Unit Testing specs2 -> https://etorreborre.github.io/specs2/ scalacheck -> https://www.scalacheck.org/
40. JUnit Interoperability -> All testing libraries available Hamkrest -> https://github.com/npryce/hamkrest Mockito-kt -> https://github.com/paslavsky/mockito-kt
41. Spek
42. Multiple inheritance
43. Interfaces • Can contain code (but not state) interface ToolbarManager {
 
 val toolbar: Toolbar
 
 fun initToolbar() {
 toolbar.inflateMenu(R.menu.menu_main)
 toolbar.setOnMenuItemClickListener {
 when (it.itemId) {
 R.id.action_settings -> App.instance.toast("Settings")
 else -> App.instance.toast("Unknown option")
 }
 true
 }
 }
 }
44. Interfaces class MainActivity : AppCompatActivity(), ToolbarManager {
 
 override val toolbar by lazy { find<Toolbar>(R.id.toolbar) }
 
 override fun onCreate(savedInstanceState: Bundle?) {
 super.onCreate(savedInstanceState)
 setContentView(R.layout.activity_main)
 initToolbar()
 ...
 }
 }

45. • Fundamental unit of code reuse in Scala • A class can mix in any number • Order matters Traits & self types
46. class MyActivity extend Activity with PresentationTrait { def onCreate() = initUi() } trait PresentationTrait { self: Activity => def initUi() = getApplicationContext } Example
47. Dependency injection
48. Cake Pattern • Dependencies between components • Traits & Self types macwire -> https://github.com/adamw/macwire scaldi -> http://scaldi.org/ Libraries Implicit • Dependencies using implicit
49. Simple injection can be done without libraries: - Interface delegation - Default values for arguments Several libraries - Dagger 2 (https://github.com/google/dagger) - Kodein (https://github.com/SalomonBrys/Kodein) - Injekt (https://github.com/kohesive/injekt)
50. Delegate handling
51. val f: (Int, String) -> String = { i, s -> "$s $i" } 
 val f = { i: Int, s: String -> "$s $i" } fun myFun(listener: (View) -> Unit) {
 ...
 listener(view)
 } Variables Function parameters
52. Higher-order function • Takes one or more functions as arguments • Returns a function as its result val f1: (Int) => String = (myInt) => myInt.toString def myFunc(f: (Int) => String) = { println(f(2)) }
53. Pattern matching
54. def toYesOrNo(choice: Int): String = choice match { case 1 => "yes" case 0 => "no" case _ => "error" } Traditional approach def get(animal: Animal): String = animal match { case cat: Cat => “I’m a cat: ” + cat.toString case dog: Dog => “I’m a dog: ” + dog.toString case _ => “Other animal" } Typed pattern
55. case class Developer(name: String, lang: String) def developer(dev: Developer): String = dev match { case Developer(_, “scala”) => “Good Dev" case Developer(“Jorge Barroso”, _) => “The best" case _ => “Java Developers" } Cases Classes def developer(dev: Developer): String = dev match { case Developer(_, “scala”) => “Good Dev" case Developer(name, _) if name.contains(“Jorge”) => “The best" case _ => “Java Developers" } If statements
56. No pattern matching, but powerful “when” val cost = when(x) {
 in 1..10 -> "cheap"
 in 10..100 -> "regular"
 in 100..1000 -> "expensive"
 in specialValues -> "special value!"
 else -> "not rated"
 }
57. val res = when {
 x in 1..10 -> "cheap"
 s.contains("hello") -> "it's a welcome!"
 v is ViewGroup -> "child count: ${v.getChildCount()}"
 else -> ""
 }
58. Learning curve from Java
59. • Really fast -> many similar concepts • Interoperability • Great official reference and Koans
61. http://scala-exercises.47deg.com/
62. Debugger
63. Debugger same as Java • Breakpoints • Step debugging • Watches • … • All inside Android Studio
64. Debugger same as Java • Breakpoints • Step debugging • Watches • … • All inside Android Studio
65. Compilation times
66. http://antonioleiva.com/plaid-kotlin-1/
67. • Slower (Scala Compiler + Proguard) • Size matters (+ ~2.8 M) Compile Take your time to setup your SBT • Incremental compiler • Continuous build and test