Oop2010 Scala Presentation Stal

Introduction toCoding in Scala is fun! OOP 2010 Dr. Michael Stal Michael.Stal@siemens.com

Objectives of this Presentation Introduce core concepts of Scala Showing you the benefits of combining OO with functional programming Illustrating the language in a pragmatic way preferring code over theory But not to cover every available aspect or to cover aspects in full detail For instance, we won‘t cover Java/Scala Interop, Views, Equality Semantics, Unit Testing, Annotations Page 2

Introduction Scala created by the team of Martin Odersky at EPFL „Scala“ means „Scalable Language“ „Scalable“ means: the same language concepts for programming in the small & large In Scala this is achieved in a pragmatic way by combining Object Oriented Programming with Functional Programming Scala is a statically typed language like Java All types are objects Page 3 Martin Odersky, Source: http://lamp.epfl.ch/~odersky/

Object-Oriented & Functional Programming Object-Oriented Programming Abstraction using Classes and Interfaces Refinement using subtyping and inheritance (Remember the Liskov Substitution Principle!) Dynamics through polymorphism Functional Programming Higher Order Functions as First-Class Entities ADTs (Abstract Data Types) following algebraic conventions Pattern matching Parametric polymorphism (generic types) Page 4 SCALA

Core Properties of Scala (see Programming in Scala) Scala is compatible: runs on JVM, interoperability with Java Scala is concise: More compact code because removal of Java boilerplate code and powerful libraries Scala is high-level: Higher level of abstraction by combining OO with functional programming Scala is statically typed Page 5 Scala‘s Roots: ,[object Object]

Stairway to Heaven – First Steps using Scala This source code file may be compiled using scalac und run using scala: scalac HelloWorldMain.scala scala HelloWorldMain Note: the source file must be named like the main object to be executed You may run an interpreter by using the following command line instead scala HelloWorldMain.scala In this case you may also use plain Scala scripts (no classes or objects required) Or, even better, you might use an IDE like Idea, Netbeans, or Eclipse Page 7

A more advanced example (1) (from Venkat Subramanian‘s book Programming Scala, pp.5) Page 8 import scala.actors._ import Actor._ val symbols = List( "AAPL", "GOOG", "IBM", "JAVA", "MSFT") val receiver = self val year = 2009 symbols.foreach { symbol => actor { receiver ! getYearEndClosing(symbol, year) } } val (topStock, highestPrice) = getTopStock(symbols.length) printf("Top stock of %d is %s closing at price %f", year, topStock, highestPrice) def getYearEndClosing(symbol : String, year : Int) = { val url = new java.net.URL("http://ichart.finance.yahoo.com/table.csv?s=" + symbol + "&a=11&b=01&c=" + year + "&d=11&e=31&f=" + year + "&g=m") val data = io.Source.fromURL(url).mkString val price = data.split("")(1).split(",")(4).toDouble (symbol, price) } // .. to be continued

A more advanced example (2)(from Venkat Subramanian‘s book Programming Scala, pp.5) Run this within interpreter mode scala TopScala.scala After the end of the talk return to this example and check whether you better understand it Page 9 // continued ... def getTopStock(count : Int) : (String, Double) = { (1 to count).foldLeft("", 0.0) { (previousHigh, index) => receiveWithin(10000) { case (symbol : String, price : Double) => if (price > previousHigh._2) (symbol, price) else previousHigh } } } // will result in => // Top stock of 2009 is GOOG closing at price 619,980000

Scala Type Hierarchy Page 10 Scala uses a pure object-oriented type system Every value is an object Two types: values and references Any is parent class of all classes, Nothing subclass of all classes Basic types like in Java Source: Scala Reference Manual

First Class Scala Page 11 born and id will be public fields Main constructor Classes in Scala contain fields, methods, types, constructors Visibility is public per default class CatID(val id : Int) //that's a whole class class Cat(val born: Int, val id: CatID) { private var miceEaten: Int = 0 def digested() = miceEaten def hunt(miceCaught: Int) { miceEaten += miceCaught } } object ScalaClasses { def main(args: Array[String]) { val id = new CatID(42) val tom = new Cat(2010, id) tom.hunt(3) tom hunt 2 println(“cat was born in “ + tom.born) println(tom.digested) } } // => 5 <> Tom was born in 2010 definition of methods No brackets required

Class Constructors Page 12 class Complex (r : Double, i: Double) { println("Constructing a complex number") val re = r val im = i def this(r : Double) = this(r,0) override def toString = re + (if (im < 0) "-" + (-im) else "+" + im) + "*i" ... } Belongs to Primary constructor Auxilliary constructorsmust call primary

Immutable and Mutable Objects Scala provides immutable objects (functional programming) but also mutable objects Immutability has many benefits Reduction of race conditions in concurrent programs Protection against unwanted modification Scala provides mutable & immutable versions of collection types Mutable objects are important to address objects that are supposed to change their state, but use them with care Page 13 class Person(var name: String) object ImmutabilityDemo { def main(args:Array[String]) = { val s = "Michael" s = "Bill" // error var t = "Michael“ // t variable t = "Bill" // ok val c = new Person("Bill") c = new Person("Tom") // error // ok - c itself unchanged: c.name = "Tom" } }

Inheritance In Scala classes can be derived from at most one base class Classes may be abstract You need to indicate whether you override inherited methods Page 14 abstractclass Shape { type Identifier = Int // defining types def getID() : Identifier = 42 def draw() : String // abstract method } class Circle (val cx: Double, val cy: Double, val r: Double) extends Shape { val id : Identifier = getID() override def draw() : String = "I am a Circle" }

Companion Objects and Standalone Objects We already saw standalone objects Objects are singletons If you need static fields or methods for a class, introduce a companion class with the same name Convention: apply() methods may be provided as factory methods Page 15 class Cat private (val born : Int, val id: CatID) { ... private def this(id: CatID) = this(2010, id) ... } // all constructors are private object Cat { // this is the companion object of Cat def apply(born: Int, id: CatID) = new Cat(born, id) def apply(id: CatID) = new Cat(id) // factory method def whatCatsDo() = "Sleep, eat, play" } object ScalaClasses { // Standalone Object def main(args: Array[String]) { val id = new CatID(43) val pussy = Cat(id) // no new required println("Pussy was born in " + pussy.born) println(Cat.whatCatsDo) // like static in Java } }

Application Base Class For experimenting with Scala use the base class Application Just compile this with: scalac ObjDemo.scala And run it with: scala ObjDemo Useful abbreviation if you do not need to deal with command line arguments Page 16 Inheritance object ObjDemoextends Application { val s: String = "Michael" println(s) // => Michael }

Traits Classes and instances may mix-in additional functionality using traits Traits represent an abstraction between interfaces and classes Using traits we can easily live with the single-inheritance restriction You may use also traits via anonymous classes: val x = new Identity{} x.name = "UFO" println(x.whoAmI) Page 17 trait Identity { var name: String="" def whoAmI() : String = name } class Person extends Identity class Animal object TraitDemo { def main(args:Array[String]) = { val p = new Person p.name = "Michael" println(p.whoAmI) val a = new Animal with Identity a.name = "Kittie" println(a.whoAmI) } } // => Michael <> Kittie

Traits and Virtual Super: Inheritance Linearization Page 18 abstract class Processor { def process() } trait Compressor extends Processor { // trait only applicable to Processor subclass abstract override def process() = { println("I am compressing"); super.process } } trait Encryptor extends Processor { // only applicable to Processor subclass abstract override def process() = { println("I am encrypting"); super.process} } class SampleProcessor extends Processor { // subclass of Processor override def process() = println("I am a Sample Processor") } object traitsample2 { def main(args:Array[String]) = { // mixing in a trait to an object: val proc1 = new SampleProcessor with Compressor with Encryptor proc1.process// Encryptor.process=>Compressor.process } // => SampleProcessor.process } Note: abstract override for a trait method means the actual subclass of Processor will provide a concrete implementation of that method!

Scala Basics: if Statements If statements are expressions themselves, i.e. they have values Page 19 import java.util._ if (1 + 1 == 3) println(“strange world”) else { println(“everything’s ok”) } val res = if ((new Random().nextInt(6) + 1) == 6) "You win!" else "You lose!"

Scala Basics: for Comprehensions (1) A for comprehension is like a for loop. It lets you traverse a collection, return every object in a temporary variable which is then passed to an expression. You may also specify nested iterations: You can specify filters for the collection elements Page 20 val aList = List(1,2,3,4,5,6) for (i <- aList) println(i) // => 1 <> 2 ... val dogs = Set("Lassie", "Lucy", "Rex", "Prince"); for (a <- dogs if a.contains("L")) println(a) // => “Lassie” <> “Lucy”

Scala Basics: for Comprehensions (2) Yield allows to create new collections in a for comprehension: You can specify filters for the collection elements Page 21 var newSet = for { a <- dogs if a.startsWith("L") } yield a println(newSet) // Set(Lassie, Lucy) for { i <- List(1,2,3,4,5,6) j = i * 2 // new variable j defined } println(j) // => 2 <> 4 <> 6 ...

Scala Basics: Other loops Scala supports while and do-while loops But generator expressions such as (1 to 6) incl. 6 or (1 until 6) excl. 6 together with for make this much easier Note: The reason this works is a conversion to RichInt where to is defined as a method that returns an object of type Range.Inclusive, an inner class of Range implementing for comprehensions Page 22 var i = 1 while (i <= 6) { println(i) i += 1 } // = 1 <> 2 <> 3 ... for (i <- 1 to 6) println(i)

Scala Basics: Exception handling try-catch-finally available in Scala but throws isn‘t catching checked exceptions is optional! catch-order important as in Java, C++ or C# Page 23 def temperature(f: Double) { if (f < 0) throw new IllegalArgumentException() } try { println("acquiring resources") temperature(-5) } catch { case ex: IllegalArgumentException => println("temperatur < 0!") case _ => println("unexpected problem") } finally { println("releasing resources") }

Inner Classes You may define inner classes as in Java Special notation (<name> =>) for referring to outer class this from an inner class: you might also use <outerclass>.this instead Page 24 class Element (val id: String){ elem => class Properties { // inner class type KV = Tuple2[String, Any] var props: List[KV] = Nil def add(entry: KV) { props = entry :: props } override def toString = { var s: String = "" for (p <- properties.props) s = s + p +"" s } } override def toString = "ID = " + id + "" + properties val properties = new Properties } object InnerClassDemo extends Application { val e = new Element("Window") e.properties.add("Color", "Red") e.properties.add("Version", 42) println(e.toString) }

Imports and Packages We can partition Scala definitions into packages: A package is a special object which defines a set of member classes, objects and packages. Unlike other objects, packages are not introduced by a definition Importing packages works via import statements – almost like in Java Packages scala, java.lang, scala.Predefare automatically imported Page 25 package MyPackage1 { class Person(val name: String) class Animal(val name: String) } import MyPackage1._ object PacDemo extends Application { val person = new Person("Michael") println(person name) } ,[object Object], to import p.* in Java). ,[object Object]

import p.{x => a} the member x of p renamed as a.

import p.{x, y} the members x and y of p.

import p1.p2.z the member z of p2, itself member of p1.,[object Object]

Advanced Types: Sets Collection Type: Set Page 27 object SetDemo { def main(args:Array[String]) { val s1 = Set[Int](1,2,3,4,5) // we could also use = Set(1,2,3,4,5) val s2 = Set[Int](2,3,5,7) println(s2.contains(3)) // => true val s3 = s1 ++ s2 // union println(s3) // => Set(5,7,3,1,4,2) vals4 = s1 & s2 // intersection: in earlier versions ** println(s4) // Set(5,3,2) } }

Advanced Types: Maps Collection Type: Map Page 28 object MapDemo { def main(args:Array[String]) { val m1 = Map[Int, String](1 -> "Scala", 2->"Java", 3->"Clojure") valm2 = m1 + (4 -> "C#") // add entry println(m2 + " has size " + m2.size) //=> Map(1->Scala,…) has size 4 println(m1(1)) // => Scala val m3 = m2 filter { element => val (key, value) = element (value contains "a") } println(m3) // => Map(1->Scala, w->Java) } }

Advanced Types: Options object DayOfWeek extends Enumeration { val Monday = Value("Monday") //argument optional val Sunday = Value("Sunday") //argument optional } import DayOfWeek._ object OptionDemo { def whatIDo(day: DayOfWeek.Value) : Option[String] = { day match { case Monday => Some("Working hard") case Sunday => None } } def main(args:Array[String]) { println(whatIDo(DayOfWeek.Monday)) println(whatIDo(DayOfWeek.Sunday)) } //=> Some(„Working Hard“) <> None } The Option type helps dealing with optional values For instance, a search operation might return a result or nothing We are also introducing Enumerationtypes Page 29

Advanced Types: Regular Expressions Type: Regex introduces well-known regular expressions Page 30 With this syntax strings remain formatted as specified and escape sequences are not required object RegDemo { def main(args:Array[String]) { val pattern = """""".r val sentence = “X was born on 01.01.2000 ?" println (pattern findFirstIn sentence) // => Some(01.01.2000) } } Note: the „r“ in “““<string>“““.r means: regular expression

Advanced Types: Tuples Tuples combine fixed number of Elements of various types Thus, you are freed from creating heavy-weight classes for simple aggregates Page 31 println( (1, "Douglas Adams", true) ) def goodBook = { ("Douglas Adams", 42, "Hitchhiker's Guide") } println ( goodBook._3 ) // get third element // => (1, Douglas Adams, true) // => Hitchhiker‘s Guide

Advanced Types: Arrays Arrays hold sequences of elements Access very efficient Page 32 val a1 = new Array[Int](5) // initialized with zeros val a2 = Array(1,2,3,4,5) // initialized with 1,2,3,4,5 println( a2(1) ) // => 2 a2(1) = 1 // => Array (1,1,3,4,5) Note: In Scala the assignment operator = does not return a reference to the left variable (e.g., in a = b). Thus, the following is allowed in Java but not in Scala: a = b = c

Smooth Operator In Scala operator symbols are just plain method names For instance 1 + 2 stands for 1.+(2) Precedence rules: All letters | ^ & < > = ! : + - * / % Page 33 class Complex(val re:Double, val im:Double) { def +(that: Complex) : Complex = { new Complex(this.re + that.re, this.im + that.im) } override def toString() : String = { re + (if (im < 0) "" else "+") + im +"i" } } object Operators { def main(args: Array[String]) { val c1 = new Complex(1.0, 1.0) val c2 = new Complex(2.0, 1.0) println(c1+c2) } } // => (3.0+2.0i)

Conversions Implicit converters allow Scala to automatically convert data types Suppose, you‘d like to introduce a mathematical notatation such as 10! Using implicit type converters you can easily achieve this Page 34 object Factorial { def fac(n: Int): BigInt = if (n == 0) 1 else fac(n-1) * n class Factorizer(n: Int) { def ! = fac(n) } implicit def int2fac(n: Int) = new Factorizer(n) } import Factorial._ object ConvDemo extends Application { println("8! = " + (8!)) // 8 will be implicitly converted } // => 40320

Parameterized Types in Scala Classes, Traits, Functions may be parameterized with types In contrast to Java no wildcards permitted – parameter types must have names Variance specification allow to specify covariance and contravariance Page 35 trait MyTrait[S,T] { def print(s:S, t:T) : String = "(" + s + "," + t + ")" } class MyPair[S,T] (val s : S, val t : T) extends MyTrait [S,T] { override def toString() : String = print(s,t) } object Generics { def main(args: Array[String]) { val m = new MyPair[Int,Int](1,1) printf(m.toString()) } } // => (1,1)

Small Detour to Variance and Covariance / Type Bounds If X[T] is a parameterized type and T an immutable type: X[T] is covariant in T if: S subTypeOf T => X[S] subTypeOf X[T] X[T] is contravariant in T if: S subTypeOf T => X[S] superTypeOf X[T] In Scala covariance is expressed as X[+T] and contravariance with X[-T] Covariance is not always what you want: Intuitively we could assign a set of apples to a set of fruits. However, to a set of fruits we can add an orange. The original set of apples gets „corrupted“ this way Example List[+T]: Covariance means a List[Int] can be assigned to a List[Any] because Int is subtype of Any Upper/Lower Bounds may be specified: In the following example D must be supertype of S: def copy[S, D>:S](src: Array[S], dst: Array[D]) = { ... Page 36

Functional Aspects: Functions and Closures In Scala Functions are First-Class Citizens They can be passed as arguments assigned to variables: val closure={i:Int => i+42} Nested functions are also supported Page 37 object scalafunctions { def add(left:Int,right:Int, code:Int=>Int)= { var res = 0 for (i<-left to right) res += code(i) res } def main(args: Array[String]) { println(add(0,10, i => i)) println(add(10,20, i => i % 2 )) } } => 55 5

Functional Aspects: Call-by-Name If a parameterless closure is passed as an argument to a function, Scala will evaluate the argument when the argument is actually used This is in contrast to call-by-value arguments A similar effect can be achieved using lazy (value) evaluation: lazy val = <expr> Page 38 import java.util._ object CbNDemo { def fun(v: => Int) : Int = v // v is a Call-by-Name Parameter def v() : Int = new Random().nextInt(1000) def main(args:Array[String]) { println( fun(v) ) println( fun(v) ) } } // => 123 <> 243

Functional Aspects: Currying (1) Currying means to transform a function with multiple arguments to a nested call of functions with one (or more) argument(s) def fun(i:Int)(j:Int) {} (Int)=>(Int)=>Unit=<function1> Page 39 object scalafunctions { def fun1(i:Int, j:Int) : Int = i + j def fun2(i:Int)(j:Int) : Int = i + j def main(args: Array[String]) { println(fun1(2,3)) println(fun2(2){3}) println(fun2{2}{3} ) } } // => 5 5 5

Functional Aspects: Currying (2) Currying helps increase readability Take foldleft as an example Page 40 FoldLeft Operator val x = (0 /: (1 to 10)) { (sum, elem) => sum + elem } // 55 Carryover value for next iteration Function arguments Carryover value Collection For each iteration, foldleft passes the carry over value and the current collection element. We need to provide the operation to be applied This is collection which we iterate over This is the value that is updated in each iteration Think how this would be implemented in Java!

Positional Parameters If you use a parameter only once, you can use positional notation of parameters with _ (underscore) instead Page 41 object scalafunctions { def main(args:Array[String]) { val seq= (1 to 10) println( (0 /: seq) { (sum, elem) => sum + elem } ) println( (0 /: seq) { _ + _ } ) } }

Using the features we can build new DSLs and additional features easily The following loop-unless example is from the Scala tutorial Page 42 object TargetTest2 extends Application { def loop(body: => Unit): LoopUnlessCond = new LoopUnlessCond(body) protected class LoopUnlessCond(body: => Unit) { def unless(cond: => Boolean) { body if (!cond) unless(cond) } } var i = 10 loop { println("i = " + i) i -= 1 } unless (i == 0) } We are calling loop with this body ... and invoking unless on the result

Functional Aspect: Partially Applied Functions If you only provide a subset of arguments to a function call, you actually retrieve a partially defined function Only the passed arguments are bound, all others are not In a call to a partially applied function you need to pass the unbound arguments All this is useful to leverage the DRY principle when passing the same arguments again and again Page 43 object scalafunctions { def fun(a : Int, b : Int, c:Int) = a+b+c def main(args: Array[String]) { val partialFun = fun(1,2,_:Int) println( partialFun(3) ) // 6 println( partialFun(4) ) // 7 } }

Functions Are Objects Function: S => T  trait Function1[-S,+T] { def apply(x:S):T } Example: (x: Int) => x * 2 -> new Function1[Int,Int] { def apply(X:Int):Int = x * 2 } In Scala all function values are objects Basically, each function is identical to a class with an apply method Thus, you can even derive subclasses from functions Array is an example for this: class Array [T] (length: Int ) extends (Int => T) { def length: Int = ... Page 44

Functional Aspects: Pattern Matching Pattern matching allows to make a pragmatic choice between various options Page 45 valaNumber = new Random().nextInt(6) + 1; aNumbermatch { case 6 => println("You got a 6") case 1 => println("You got a 1"); caseotherNumber => println("It is a " + otherNumber) }

Functional Aspects: Matching on Types It is also possible to differentiate by type: Page 46 object TypeCase { def matcher(a: Any) { a match { case i : Int if (i == 42) => println("42") case j : Int => println("Another int") case s : String => println(s) case _ => println("Something else") } } def main(args: Array[String]) { matcher(42) matcher(1) matcher("OOP") matcher(1.3) } } // => 41 <> 1 <> OOP <> Something else

Functional Aspects: Matching on Lists Lists can be easily used with Pattern Matching: Page 47 object ListCase { def matcher(l: List[Int]) { l match { case List(1,2,3,5,7) => println("Primes") case List(_,_,_3,_) => println("3 on 3"); case 1::rest => println("List with starting 1"); case List(_*) => println("Other List"); } } def main(args: Array[String]) { matcher(List(1,2,3,5,7)) matcher(List(5,4,3,2)) matcher(List(1,4,5,6,7,8)); matcher(List(42)) } } => Primes <> 3 on 3 <> List with starting 1 <> Other List

Functional Aspects: Matching on Tuples So do Tuples: Page 48 object TupleCase { def matcher(t : Tuple2[String,String]) { t match { case ("OOP",s) => println("OOP " + s) case ("Scala", s) => println("Scala " + s) case _ => println("Other Tuple") } } def main(args: Array[String]) { matcher("OOP", "2010") matcher("Scala", "rocks"); matcher("A","B") } } => OOP 2010 <> Scala rocks >cr> Other Tuple

Functional Aspects: Matching on Case Classes Case Classes are classes for which the compiler generates additional functionality to enable pattern matching, e.g., an apply() method: Page 49 sealed abstract class Shape // sealed => subclasses only in this source file case class Circle(val center: Point, val radius: Double) extends Shape case class Line(val pt1: Point, val pt2: Point) extends Shape case class Point (val x:Double, val y:Double){ override def toString() = "(" + x +"," + y + ")" } object CaseClasses { def matcher(s : Shape) { s match { case Circle(c, r) => println(“Circle“ : + c + “ “ + r) case Line(p1, p2) => println("Line " + p1 + " : " + p2) case _ => println("Unknown shape") } } def main(args: Array[String]) { matcher(Circle(Point(1.0, 1.0), 2.0)) matcher(Line(Point(1.0, 1.0), Point(2.0, 2.0))) } }

Functional Aspect: Extractors Extractors are objects with an unapply method used to match a value and partition it into constituents – an optional apply is used for synthesis Page 50 object EMail { def apply(prefix: String, domain: String) = prefix + "@" + domain def unapply(s: String): Option[(String,String)] = { val parts = s split "@" if (parts.length == 2) Some(parts(0), parts(1)) else None } } object scalafunctions { def main(args:Array[String]) { val s = "michael.stal@siemens.com" s match { case EMail(user, domain) => println(user + " AT " + domain) case _ => println("Invalid e-mail") } } }

Partial Functions Partial Functions are not defined for all domain values Can be asked with isDefinedAt whether a domain value is accepted Example: Blocks of Pattern Matching Cases Page 51 trait PartialFunction[-D, +T] extends (D => T) { def isDefinedAt(x: D): Boolean }

Actors Actors have been introduced in the 1970s: the Actor model is a mathematical model of concurrent computationthat treats "actors" as the universal primitives of concurrent digital computation: in response to a message that it receives, an actor can make local decisions, create more actors, send more messages, and determine how to respond to the next message received. [Hewitt, 73] Page 52 Also available in Erlang, Axum, Io, Clojure Provided as library implementation in Scala (demonstrating Scala‘s capability of providing internal DSLs)

Actor Classes Class Actor requires to override act() which is the functionality executed by a thread You may also instantiate anonymous actors in a much more convenient way: Page 53 import scala.actors.Actor class VolcanextendsActor { def act() { println(“thinking ...") } } object SpockRunner { def main(args:Array[String]) = { valspock = new Volcan spock start } } import scala.actors.Actor import Actor._ object SpockRunner { def main(args:Array[String]) = { val spock = actor { println("thinking ...") } } }

Actors that communicate An actor is useless unless it cooperates with other actors Actors communicate via messages In Scala‘s actor library messages are processed in FIFO order Every actor owns an inbound and an outbound mailbox Page 54

Communicating Actors - Example Page 55 ! Note: react & receive have cousins with timeout arguments: receiveWithin and reactWithin import scala.actors._ import Actor._ object Calculator extends Actor { def fib(n: Int) : Int = { require(n >= 0) // this is a precondition if (n <= 1) n else fib(n-2) + fib(n-1) } def act() { loop { react { // or receive if thread must preserve call-stack case i:Int => actor {println("Fibonacci of "+i+" is "+fib(i))} case s:String if (s == „exit") => {println(„exit!"); exit} case _ => println("received unknown message") } } } } object ActorDemo extends Application { Calculator.start // start Actor for (i <- 0 to 30) Calculator ! i // here we send a msg to the actor Calculator ! "exit" }

Oop2010 Scala Presentation Stal

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

En vedette

En vedette (13)

Similaire à Oop2010 Scala Presentation Stal

Similaire à Oop2010 Scala Presentation Stal (20)

Dernier

Dernier (20)

Oop2010 Scala Presentation Stal