1. ScalaLorenzo DemattTrenta3devMateriale basato su esempi diAlf Kristian Style, Micheal Stal, ed altri

2. If I were to pick a language to use on the JVMtoday other than Java, it would be Scala. James Gosling, creator of Javahttp://www.adam-bien.com/roller/abien/entry/java_net_javaone_which_programmingScala, it must be stated, is the current heir apparent to theJava throne. No other language on the JVM seems ascapable of being a "replacement for Java" as Scala, andthe momentum behind Scala is now unquestionable. Charlies Nutter, JRuby leadhttp://blog.headius.com/2009/04/future-part-one.htmlMy tip though for the long term replacement of javac is Scala.Im very impressed with it! I can honestly say if someone hadshown me the Programming in Scala book [] back in 2003Id probably have never created Groovy. James Strachan, creator of Groovyhttp://macstrac.blogspot.com/2009/04/scala-as-long-term-replacement-for.html 3. Agenda Cosa , e perch Scala? Introduzione a Scala Sintassi di base Pattern matching Funzioni! Classi, traits e mixins Qualche chicca NON in queste slides (una prossima volta?): Continuations For-comprehensions and Monads Parallelismo e Actors 4. Scala Porgrammazione object oriented E funzionale Tipizzazione statica Compatibile (interoperabile) con Java Compilazione in bytecode Java Conversioni automatiche (collection, tipi base) Mixed compilation! e con .NET! Un java migliore? 5. public class Person {private int age;private String name;public Person(int age, String name) {this.age = age;this.name = name;}public int getAge() {return this.age;}public void setAge(int age) {this.age = age;}public String getName() {return this.name;}public void setName(String name) {this.name = name;}}class Person(var age: Int, var name: String) 6. List persons = ...List adults = new LinkedList();List kids = new LinkedList();for (Person person : persons) {if (person.getAge() < 18) {kids.add(person);} else {adults.add(person);}}val persons: List[Person] = ...val (kids, adults) = persons.partition(_.age < 18) 7. using(new BufferedReader(new FileReader("f.txt"))) {reader => println(reader.readLine())}BufferedReader reader = null;try {reader = new BufferedReader(new FileReader("f.txt"));System.out.println(reader.readLine());} finally {if (reader != null) {try {reader.close();} catch (IOException e) {// Exception on close, ignore}}} 8. TipiScalas: Stringi: IntJavaString sint i / Integer i 9. Variabilivar i: Int = 42 10. Variabilivar i = 42 // type inferencei = 3i = "Hello world!" // tipizzazione statica 11. Valori (~costanti)val i = 42i = 3 // errore di compilazione 12. Valori (~costanti)class DbImport(private val config: Config,private val connection:() => java.sql.Connection,...) {val db = Database(config,useSessionFactory = false,useConnectionPool = false)...Readonly/const (ma non propagato) 13. Metodidef sum(a: Int, b: Int): Int = {return a + b} 14. Metodidef sum(a: Int, b: Int): Int = {a + b} 15. Metodidef sum(a: Int, b: Int) = {a + b} 16. Metodidef sum(a: Int, b: Int) = a + b 17. Metodipublic String hello;public String getHello(){ }public void setHello(String s) { } 18. Metodipublic String hello;public String getHello(){ }public void setHello(String s) { }val hello = hello // val s = obj.hellodef hello = {println("Hello, " + name)return hello} // val s = obj.hello 19. MetodiScala:myObject.myMethod(1)myObject myMethod(1)myObject myMethod 1myObject.myOtherMethod(1, 2)myObject myOtherMethod(1, 2)myObject.myMutatingMethod()myObject.myMutatingMethodmyObject myMutatingMethodJava:myObject.myMethod(1);myObject.myOtherMethod(1, 2);myObject.myMutatingMethod() 20. Metodi"apple".charAt(0)"apple" charAt 01.0.+(2.0)1.0 + 2.0 21. Metodi"apple".charAt(0)"apple" charAt 01.0.+(2.0)1.0 + 2.0trait NumericalExpression[A] extends TypedExpressionNode[A] {def ===[B](b: NumericalExpression[B]) =new EqualityExpression(this, b)...def > [B](b: NumericalExpression[B]) = gt(b)...def +[B](b: NumericalExpression[B]) = plus(b)...def gt [B](b: NumericalExpression[B]) =new BinaryOperatorNodeLogicalBoolean(this, b, ">")...table.deleteWhere(ob => ob.tr_id === t.id and ob.data gt data) 22. Collectionsval list = List("apple", "orange", "banana")val map = Map(1 -> "uno", 2 -> "due")val array = Array(1, 2, 3, 4, 5)list(1) // orangemap(2) // duearray(3) // 4 23. myObject match {case 1 => println("Primo")case 2 => println("Secondo")case _ => println("Orru...")}Pattern matching 24. myObject match {case i: Int => println("Un numero " + I * 2)case s: String => println("Del testo " + s.toUpper)case _ => println("Orru...")}Pattern matching 25. val email = """(.+)@(.+)""".r"scala@java.no" match {case email(name, domain) =>println("User " + name + " at " + domain)case x => println(x + " is not an email")}Pattern matching 26. val numbers = List(1, 2, 3)val secondNumber = numbers match {case List(_, i, _*) => Some(i)case _ => None}=> secondNumber: Option[Int] = Some(2)Pattern matching 27. FunzioniPredicate even = new Predicate() {@Overridepublic boolean apply(Integer i) {return i % 2 == 0;}};List numbers = // 1, 2, 3, 4Iterable evenNums =Iterables.filter(numbers, even);=> [2, 4]Google collections: 28. Funzionival even = (i: Int) => i % 2 == 0val numbers = List(1, 2, 3, 4)val evenNums = numbers.filter(even)=> List(2, 4)Scala collections: 29. Funzionival numbers = List(1, 2, 3, 4)val evenNums = numbers.filter((i: Int) => i % 2 == 0)=> List(2, 4)Scala collections: 30. Funzionival numbers = List(1, 2, 3, 4)val evenNums = numbers.filter(i => i % 2 == 0)=> List(2, 4)Scala collections: 31. Funzionival numbers = List(1, 2, 3, 4)val evenNums = numbers.filter(_ % 2 == 0)=> List(2, 4)Scala collections: 32. FunzioniPredicate even = new Predicate() {@Overridepublic boolean apply(Integer i) {return i % 2 == 0;}};val evenNums = numbers.filter(_ % 2 == 0) 33. FunzioniPredicate even = i -> i % 2 == 0Java8 lambda expressions:val even = (i: Int) => i % 2 == 0Scala functions: 34. FunzioniIterables.filter(numbers, i -> i % 2 == 0)Java8 lambda expressions:numbers.filter(_ % 2 == 0)Scala functions: 35. Funzioni: cittadini di prima classeval even = Function[Int, Boolean] {def apply(i: Int) = i % 2 == 0}val even: (Int => Boolean) = (i: Int) => i % 2 == 0val even = (i: Int) => i % 2 == 0even.apply(42) // trueeven(13) // false 36. Funzioni e collectionsnumbers.filter(i => i > 2) // List(3, 4, 5)numbers.find(i => i > 2) // Some(3)numbers.exists(i => i > 2) // truenumbers.forall(i => i > 2) // falsenumbers.map(i => i * 2) // List(2, 4, 6, 8, 10)numbers.foldLeft(0) { (a, b) => a + b } // 15 37. Interfacce funzioniali e lambdahelloButton.addActionListener(e =>println(Hello World!)) 38. Closuresval people = List(Person(Alice), Person(Orru))val name = Orruval nameFilter = (p: Person) => p.name == namepeople.filter(nameFilter) // Person(Orru) 39. Closuresval people = List(Person(Alice), Person(Orru))var name = Orruval nameFilter = (p: Person) => p.name == namepeople.filter(nameFilter) // Person(Orru)name = Alicepeople.filter(nameFilter) // Person(Alice) 40. Funzioni di ordine superiore Funzioni che prendono funzioni comeparametri e/o ritornarno funzionidef test(numbers: List[Int], f: Int => Boolean) =numbers.map(tall => f(tall))// List[Boolean] 41. call-by-value vs. call-by-name by-value: espressioni valutate prima dellachiamata by-name: espressioni valutate allinterno delchiamante Quando la valutazione e costosa, non semprenecessaria; per avere computazioni on-demandcomputing Simile a lazy (che, tra parentesi, pure ce inScala) APIs performanti, e intuitive particolarmente per lecollection 42. call-by-value vs. call-by-nameExample: Loggingdef thisTakesTime(): String = {// leeento! Prende la stringa dal DB magari!}def debug(s: String) {println(debug)if (logLevel String) {println(debug)if (logLevel (that: A): Boolean = (this compare that) > 0def = 0} 51. Ordered traitclass Person(val age: Int) extends Ordered[Person] {def compare(other: Person) = this.age - other.age}val person1 = new Person(21)val person2 = new Person(31)person1 < person2 // trueperson1 = person2 // false 52. Generici Ricordate lequivalenza strutturale? 53. Dynamic mixinsclass Person(val name: String, val age: Int) {override def toString = "My name is " + name}trait Loud {override def toString = super.toString.toUpperCase}val person = new Person("Orru", 18) with Loudprintln(person)=> MY NAME IS ORRU 54. using(new BufferedReader(new FileReader("f.txt"))) {reader => println(reader.readLine())}BufferedReader reader = null;try {reader = new BufferedReader(new FileReader("f.txt"));System.out.println(reader.readLine());} finally {if (reader != null) {try {reader.close();} catch (IOException e) {// Exception on close, ignore}}}Ricordate? 55. def using[T A) = {try {f(closeable)} finally {if (closeable != null) {try {closeable.close()}catch {case e: Exception => // Do something clever!?}}}} 56. For-loopsScala:for (i 0.0 60. Imparare scala Sintassi... dipende! E facile scrivere Java-ish Scala Il linguaggio cresce man mano che lo capiete Vi lascia migrare gradualmente a uno stile piufunzionale Vi lascia mantenere strtuttura! Ha delle chicche prese singolarmente, niente di che Insieme... 61. Programmazione funzionale pura Funzioni matematiche Niente side effects In pratica: solo oggetti immutabili Tutti i campi sono immutabili (val) Le chiamate ai metodi non hanno side-effects Eh? Hint: producono un nuovo oggetto => tutti i metodi ritornano qualcosa, un valore! 62. Esempio: scala.List head :: tailval list = List(1, 2)val myList = 1 :: 2 :: Nil// 0 :: 1 :: 2 :: Nilval myotherList = 0 :: myList 63. Cercare di essere puri Concorrenza Iterator.par. Facile evitare errori NullPointerException Facile da testare scala.collection.immutable ...oppure scala.collection.mutable!