Why Kotlin is your next language?

Why Kotlin is your next language?

• 1.
  Why Kotlin isyour next language? theory and practice Aliaksei Zhynhiarouski 1 Dev Day MiniQ, 2016
• 2.
  Kotlin Island 2
• 3.
  Why is Kotlin •Static Typing bit.ly/st-vs-dyn • Java + Kotlin = ❤. 
 Effortless mixing both in one project • Java Interoperability. 
 100% interoperable with Java. 3
• 4.
  Why is Kotlin •Null Safety • Type Inference • Immutability in the mind • fun 4
• 5.
  fun main(args :Array<String>) { println("Hello, MiniQ!") } 5
• 6.
  val from_value :Type var from_variable : Type val i_am_string = “mobile” var i_am_long = 666L val i_am_double = 3.14e10 6 val & var
• 7.
  Null Safety // can’tbe null
 val foo: String = “Dev Day” 
 // need always perform the check 
 val bar: String? = null 7 Type? = Type or null
• 8.
  Null Safety val bar:String? = “Dev Day” 
 var a = bar?.length // 6
 
 var b = bar?.length?.inc() // 7
 
 var c = bar!!.length // can be NPE 8
• 9.
  Null Safety val bar:String? = null 
 var a = if (bar != null) bar.length
 else 0 // 0
 
 var b = bar?.length ?: 0 // 0
 9
• 10.
  Type Definition class Phone(valbrand: String) 10 • concise syntax for constructor • properties – not fields • final by default. Use open to open • simple old java class under the hood
• 11.
  Type Definition class Phone(valbrand: String){ var version: Int = 0 } 11 get() {…}
 private set val phone = Phone(“Apple”)
 phone.brand == “Apple” // true
• 12.
  Value Object data classPhone(val brand: String) 12 toString() hashCode() equals()
 copy()
• 13.
  Get ready tobe inspired 13
• 14.
  Extensions 14 // Usage Example
 
 “MiniQ”.lastChar()// “Q”
 // Definition
 
 fun String.lastChar():Char 
 = this.get(length - 1)
• 15.
  Extensions 15 // Java underthe hood
 
 @file:JvmName(“StringUtils")
 StringUtils.lastChar(“Mobile”);
• 16.
  Extensions 16 Collections.max(list)
 
 ↓ list.max()
• 17.
  Extensions 17 operator fun BigDecimal.inc()
 = this + BigDecimal.ONE 
 // Example
 var counter = BigDecimal.ZERO
 
 print(++counter) // 1
• 18.
  Extensions 18 “25”.toInt() // Int “8.$minor.5”.toOsVersion()// to object
• 19.
  Android Extensions 19 val text= find<TextView>(R.id.text) Just extend Activity and have fun inline fun <reified T : View> 
 Activity.find(id: Int): T = this.findViewById(id) as T final TextView text = (TextView) v.findViewById(R.id.text);
• 20.
  Lambdas 20 val boys =listOf(
 Boy(“Alex”), Boy(“Petr”), Boy(“Oleg”))
 // 1 
 boys.filter({ b: Boy -> b.age > 18 })
 // 2
 boys.filter({ it.age > 18 }) 
 // 3
 boys.filter { it.age > 18 }
• 21.
  λ 21 boys.filter { it.age> 18 } .map { Pair(it, Boy("Eugene")) } .forEach { dance(it) } // Definition
 
 inline fun <T> Iterable<T>.filter
 (predicate: (T) -> Boolean)

• 22.
  λ 22 db.inTransaction {
 delete(“users”, “name= ?”, arrayOf(“Alex”))
 } fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit) { beginTransaction() try {
 func()
 setTransactionSuccessful() } finally { endTransaction() } }
• 23.
  Delegates – rightway 23 class View {
 
 
 
 
 
 
 
 } val lazyProp by lazy { “Dev Day” } val ops by observable(“”) { 
 prop, old, new -> print("$old to $new") }
• 24.
  Delegates – wowway 24 class Activity {
 
 
 
 
 
 
 } private val btn: Button by lazy {
 findViewById(R.id.btn) as Button
 }
 
 override fun onCreate(savedBundle: Bundle?) {
 btn.setText(“MiniQ!”)
 } 

• 25.
  Delegates – wowway 25 class Query(val props: Map<String, String>) {
 
 } val category by props
 val model by props
 
 val info: String
 get() {
 return “$category - $model” 
 }
• 26.
  Delegates – wowway 26 class Query(val props: Map<String, String>) {
 
 } val category by props
 val model by props
 …
 val props = mapOf(“category” to “XXX”,
 “model” to “YYY”)
 val query = Query(props) print(query.info) // “XXX - YYY”

• 27.
  DSL 27 • Type-safe • Expressyour code by flexible syntax • Ideal to build own query engine • if/for/when just inside DSL
• 28.
  DSL 28 "(#C1 = :active)AND (#C2 = :type) AND " + "(attribute_not_exists(#C1) OR #C1 IN (:model, :allModels)) AND " +
 "...";
 if (smth)
 append("(#C2 = :active) AND NOT contains(#C3, :brandAll)"); … // wait, oh shi~
• 29.
  DSL 29 val expr =filterExpr {
 group {
 eq("#1", ":2") and eq("#1", ":2") 
 or group {
 eq("#2", ":2")
 if (smth) { 
 and eq("#2", ":2") 
 }
 }
 and ……
 }
• 30.
  One more DSLthing 30 Gradle 3 meets Kotlin
• 31.
  Kotlin 1.1 typealias Callback<T>= (T) -> T // And now
 fun alias(cb: Callback<String>) {} 31 Type aliases
• 32.
  Kotlin 1.1 typealias Table<K>= 
 
 MutableMap<K, MutableList<String>> 32 Type aliases
• 33.
  Kotlin 1.1 val future= async<String> { (1..5).map { await(loooongAsyncOperation(it))
 
 }.joinToString("n") } 33 Coroutines with async/await
• 34.
  Why is Kotlin •Use all existing Java frameworks and libraries • Code reviews are not a problem • Suitable for enterprise Java • Adopting is low risk 34
• 35.
  Why is Kotlin •Android • Gradle • Can be learned in a few hours • Kotlin also compiles to JavaScript ;) 35
• 36.
  http://try.kotl.in 36
• 37.
  Links Awesome Kotlin kotlin.link Slack kotlinlang.slack.com Local’sChat gitter.im/JavaBy/Kotlin 37
• 38.
  Links just foryou Kotlin compilation speed Performance: Kotlin Bytecode https://www.youtube.com/watch?v=eQ4YHpAXdp4 Experience of Square with Kotlin. Good analysis Android Development advanced https://vimeo.com/144877458 Kotlin in real project with a lot of nuances https://www.youtube.com/watch?v=CABN2r4GPpQ 38
• 39.
  Kotlin friends 39 jprof.by bkug.by
• 40.
  Go v Minsk,ja sozdal