Scala uma poderosa linguagem para a jvm

Scala

Uma poderosa linguagem para a JVM

Isaías Cristiano Barroso
Strategia Tecnologia

29 de Maio de 2012

 Criador da linguagem Scala

 Compilador de Referência JAVA

 Co-autor Java Generics

Martin Odersky
EPFL - École polytechnique fédérale de Lausanne

Scala – O que disse James Gosling?

"If I were to pick a language
to use today other than Java,
it would be Scala."
-- James Gosling, criador do Java

Scala – Visão Geral

 Compatibilidade com a JVM (JDK 1.5+)

 Linguagem funcional

 Empresa Typesafe (www.typesafe.com) mantem
junto a comunidade a linguagem Scala.

Scala – Comparação de Byte Code

public class Hello { class Hello {
public String sayHello(String name){ def sayHello(name: String):String = {
return "Hello " + name; "Hello " + name
} }
} }

Código JAVA vs Scala

Scala – Comparação de Byte Code

public class Hello extends public class Hello extends Object
java.lang.Object{ implements scala.ScalaObject{
public Hello(); public java.lang.String
Code: sayHello(java.lang.String);
0: aload_0 Code:
1: invokespecial #1; //Method 0: new #7; //class
java/lang/Object."<init>":()V scala/collection/mutable/StringBuilder
4: return 3: dup
4: invokespecial #11; //Method
public java.lang.String scala/collection/mutable/StringBuilder."<i
sayHello(java.lang.String); nit>":()V
Code: 7: ldc #14; //String Hello
0: new #2; //class 9: invokevirtual #18; //Method
java/lang/StringBuilder scala/collection/mutable/StringBuilder.app
3: dup end:(Ljava/lang/Object;)Lscala/collection/
4: invokespecial #3; //Method mutable/StringBuilder;
java/lang/StringBuilder."<init>":()V 12: aload_1
7: ldc #4; //String Hello 13: invokevirtual #18; //Method
9: invokevirtual #5; //Method scala/collection/mutable/StringBuilder.app
java/lang/StringBuilder.append:(Ljava/lang/ end:(Ljava/lang/Object;)Lscala/collection/
String;)Ljava/lang/StringBuilder; mutable/StringBuilder;
12: aload_1 16: invokevirtual #22; //Method
13: invokevirtual #5; //Method scala/collection/mutable/StringBuilder.toS
java/lang/StringBuilder.append:(Ljava/lang/ tring:()Ljava/lang/String;
String;)Ljava/lang/StringBuilder; 19: areturn
16: invokevirtual #6; //Method public Hello();
java/lang/StringBuilder.toString: Code:
()Ljava/lang/String; 0: aload_0
19: areturn 1: invokespecial #30; //Method
java/lang/Object."<init>":()V
} 4: return
}

Scala – Orientada a Objetos

Cada valor é um objeto


Cada valor é um objeto

scala> val a = 10
a: Int = 10

scala> a.
% & * + -

/ > >= >> >>>

^ asInstanceOf isInstanceOf toByte toChar

toDouble toFloat toInt toLong toShort

toString unary_+ unary_- unary_~ |

scala> a.+(10)
res0: Int = 20

scala> a + 10
res1: Int = 20


Classes

class Point(xc: Int, yc: Int) {
var x: Int = xc
var y: Int = yc
def move(dx: Int, dy: Int) {
x = x + dx
y = y + dy
}
override def toString(): String = "(" + x + ", " + y + ")";
}

scala> val p = new Point(10, 20)
p: Point = (10, 20)

scala> p
res0: Point = (10, 20)


Classes (Scala vs JAVA)
class Point(xc: Int, yc: Int) {
var x: Int = xc
var y: Int = yc
def move(dx: Int, dy: Int) {
x = x + dx
y = y + dy
}
override def toString(): String = "(" + x + ", " + y + ")";
}
public class Point {
int x;
int y;
Point(int xc, int yc){
x = xc;
y = yc;
}
public void move(int dx, int dy){
x = x + dx;
y = y + dy;
}
public String toString() {
return "(" + x + ", " + y + " )";
}
}


Traits

Utilizadas para definir tipos e métodos suportados de um
objeto

Similar as interfaces JAVA

Podem ser parcialmente implementadas

Não tem parâmetros para construtores


Traits
trait Similarity {
def isSimilar(x: Any): Boolean
def isNotSimilar(x: Any): Boolean = !isSimilar(x)
}

class Point(xc: Int, yc: Int) extends Similarity {
var x: Int = xc
var y: Int = yc
def isSimilar(obj: Any) =
obj.isInstanceOf[Point] &&
obj.asInstanceOf[Point].x == x
}

object TraitsTest extends Application {
val p1 = new Point(2, 3)
println(p1.isNotSimilar(p2)) // false
println(p1.isNotSimilar(p3)) // true
println(p1.isNotSimilar(2)) // true
}


“object”

Equivalente a uma Singleton class to Java

…

object TraitsTest extends Application {
println(p1.isNotSimilar(p2)) // false
println(p1.isNotSimilar(p3)) // true
println(p1.isNotSimilar(2)) // true
}


“Companion Object”

Mesmo nome da classe

Definido no mesmo arquivo da classe

Possui acesso a todos os membros da classe

Muito utilizado como Factory

http://www.scala-lang.org/api


“Companion Object”

http://www.scala-lang.org/api


“object”

scala> val bd = BigDecimal("123.43")
bd: scala.math.BigDecimal = 123.43

scala> val bd = BigDecimal(123.43)

“apply Method”

scala> val bd = BigDecimal.apply("123.43")

scala> val bd = BigDecimal.apply(123.43)

“Case Class”


Classes Scala como qualquer outra

Exportam seus parâmetros de construtores

Método apply criado automaticamente

Permite decomposição funcional através de “pattern
matching”


“Case Class”
scala> abstract class Pessoa
defined class Pessoa

scala> case class PessoaFisica(nome: String, idade: Int) extends
Pessoa
defined class PessoaFisica

scala> case class PessoaJuricia(nome: String, tempoAbertura: Int)
extends Pessoa
defined class PessoaJuricia
toString implementado automaticamente
scala> val pf = PessoaFisica("Joao", 83)
pf: PessoaFisica = PessoaFisica(Joao,83)

scala> val pj = PessoaJuridica("The Corp", 4)
pj: PessoaJuridica = PessoaJuridica(The Corp,4)

scala> println(pf)
PessoaFisica(Joao,83)

scala> println(pj)
PessoaJuridica(The Corp,4)


“Case Class”
equals implementado automaticamente
scala> val x = PessoaFisica("Joao", 83)
x: PessoaFisica = PessoaFisica(Joao,83)

scala> val y = PessoaFisica("Joao", 83)
y: PessoaFisica = PessoaFisica(Joao,83)

scala> val z = PessoaFisica("Maria", 78)
z: PessoaFisica = PessoaFisica(Maria,78)

scala> x == y
res3: Boolean = true

scala> x == z
res4: Boolean = false

apply de case class em ação
scala> val pf = PessoaFisica("Isaias")
<console>:9: error: not enough arguments for method apply: (nome:
String, idade: Int)PessoaFisica in object PessoaFisica.
Unspecified value parameter idade.
val pf = PessoaFisica("Isaias")


“Pattern Matching”

def testPM(p: Pessoa){
p match {
case PessoaFisica(nome, idade) =>
println("Nome: " + nome)
println("Idade: " + idade)
case PessoaJuridica(nome, tempo) =>
println("Nome: " + nome)
println("Tempo: " + tempo)
case _ =>
println("Tipo Nao Esperado")
}
}

“Sealed Case Class”
scala> sealed abstract class Pessoa
defined class Pessoa

Scala – Linguagem Funcional


High Order Functions (Funções podem receber e
retornar funções)

Programação concorrente

Encoraja a utilização de variáveis imutáveis (var x val)

Estaticamente tipada


Fatorial
def fac(n : Int) = {
var r = 1
for (i <- 1 to n) r = r * i
r
}

scala> fac(5)
res0: Int = 120

Fatorial - Recursivo
def fac(n: Int): Int =
if (n <= 0) 1
else Não
n * fac(n – 1) Otimizado
scala> fac(5)
res0: Int = 120


@tailrec
def fac(n: Int): Int =
if (n <= 0) 1
else
n * fac(n – 1)
<console>:10: error: could not optimize @tailrec annotated method
fac: it contains a recursive call not in tail position
if (n <= 0) 1
else
n * fac(n -1)
^

Fatorial – Tail Recursive

@tailrec def factorial(accumulator: Int, number: Int) : Int = {
if(number == 1)
return accumulator
factorial(number * accumulator, number - 1)
} Otimizado


Melhorando a função
def factorial(number: Int) : Int = {
def factorialWithAccumulator(accumulator: Int, number: Int) : Int
= {
if (number == 1)
return accumulator
else
factorialWithAccumulator(accumulator * number, number - 1)
}
factorialWithAccumulator(1, number)
}


Functions
def <nome>(parametros) : <retorno>
def funcao1() {
println(“Funcao sem parametro e sem retorno”)
}

def funcao2(x: Int, y: String) {
println(“Funcao com parametro e sem retorno”)
}

def funcao3(x: Int, y: String) = {
println(“Funcao com parametros e retorno implicito”)
“retorno”
}

def funcao4(x: Int, y: String):String = {
println(“Funcao com parametros e retorno explicito”)
“retorno”
}


Funções Anônimas
scala> (x: Int) => x + 1
res0: Int => Int = <function1>

scala> res0(1)
res1: Int = 2

Funções como valores
scala> val inc = (x: Int) => x + 1
inc: Int => Int = <function1>

scala> inc(10)
res0: Int = 11


High Order Functions
scala> def soma(x:Int, y:Int):Int = {
| x+y
| }
soma: (x: Int, y: Int)Int

scala> soma(10,20)
res5: Int = 30

scala> def withLog(f:(Int, Int) => Int, x:Int, y:Int):Int = {
| println("Iniciando execucao da funcao")
| val result = f(x,y)
| println("Finalizando Execucao")
| result
| }
withLog: (f: (Int, Int) => Int, x: Int, y: Int)Int

scala> withLog(soma, 10, 20)
Iniciando execucao da funcao
Finalizando Execucao
res6: Int = 30


Querulous
queryEvaluator.transaction { transaction =>
transaction.select("SELECT ... FOR UPDATE", ...)
transaction.execute("INSERT INTO users VALUES (?, ?)", 1,
"Jacques")
transaction.execute("INSERT INTO users VALUES (?, ?)", 2, "Luc")
}
//
def transaction[T](f: Transaction => T) = {
withTransaction { transaction =>
transaction.begin()
try {
val rv = f(transaction)
transaction.commit()
rv
} catch {
case e: Throwable =>
transaction.rollback()
throw e
}
}
}
private def withTransaction[A](f: Transaction => A) = {
database.withConnection { connection => f(new
Transaction(queryFactory, connection)) }
}


Implicit Parameters
scala> def addOne(implicit x:Int) = {
| x+1
| }
addOne: (implicit x: Int)Int

scala> addOne
<console>:9: error: could not find implicit value for parameter x:
Int
addOne
^

scala> implicit val x = 10
x: Int = 10

scala> addOne
res1: Int = 11

scala> addOne(35)
res2: Int = 36


Implicit Conversions
scala> class RichString(s:String)
defined class RichString

scala> implicit def string2RichString(s:String) = new RichString(s)
string2RichString: (s: String)RichString

scala> val x = "Isaias"
x: java.lang.String = Isaias

scala> def printString(r: RichString) {
| println(r)
| }
printString: (r: RichString)Unit

scala> printString(x)
$line1.$read$$iw$$iw$RichString@6fafc4c2

scala>


Mixin Class Composition
abstract class AbsIterator {
type T
def hasNext: Boolean
def next: T
}

trait RichIterator extends AbsIterator {
def foreach(f: T => Unit) { while (hasNext) f(next) }
}

class StringIterator(s: String) extends AbsIterator {
type T = Char
private var i = 0
def hasNext = i < s.length()
def next = { val ch = s charAt i; i += 1; ch }
}

object StringIteratorTest {
def main(args: Array[String]) {
class Iter extends StringIterator(args(0)) with RichIterator
val iter = new Iter
iter foreach println
}
}

Scala – Collections

Lists
val numbers = List(1, 2, 3, 4)
numbers: List[Int] = List(1, 2, 3, 4)

Sets
scala> Set(1, 1, 2)
res0: scala.collection.immutable.Set[Int] = Set(1, 2)


Tuplas
scala> val hostPort = ("localhost", 80)
hostPort: (String, Int) = (localhost, 80)

scala> hostPort._1
res5: java.lang.String = localhost

scala> hostPort._2
res6: Int = 80

Tuplas – Pattern Matching
hostPort match {
case ("localhost", port) => ...
case (host, port) => ...
}


Map
Map(1 -> 2)
res0: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2)

Map("foo" -> "bar")
res0:
scala.collection.immutable.Map[java.lang.String,java.lang.String] =
Map(foo -> bar)

Map(1 -> Map("foo" -> "bar"))
res0:
scala.collection.immutable.Map[Int,scala.collection.immutable.Map[jav
a.lang.String,java.lang.String]] = Map(1 -> Map(foo -> bar))


Option
val map = Map("Hi" -> "Dan", "Hello" -> "Jane")
val result = map.get( "Hello" )

result match {
case None => println("No value found for key!")
case Some(x) => print("Found value" + x)
}

scala> map.get("NoKey")
res5: Option[java.lang.String] = None


Functional Combinators
“A saída de uma função será utilizada como entrada para outra
função”
scala> val numbers = List(1, 2, 3, 4)
numbers: List[Int] = List(1, 2, 3, 4)

scala> numbers.map((i:Int) => i * 2)
res0: List[Int] = List(2, 4, 6, 8)

scala> numbers.map(_ * 2)

scala> numbers.foreach((i: Int) => i * 2) // Sem retorno

scala> var value = 0
value: Int = 0

scala> numbers.foreach((i: Int) => value = i*2)

scala> value
res1: Int = 28


scala> numbers.filter((i: Int) => i%2==0)
res0: List[Int] = List(2, 4)

scala> def isEven(i: Int): Boolean = i % 2 == 0
isEven: (i: Int)Boolean

scala> numbers.filter(isEven _)
res2: List[Int] = List(2, 4)

scala> List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10).partition((i: Int) => i >
5)
res0: (List[Int], List[Int]) = (List(6, 7, 8, 9, 10),List(1, 2, 3, 4,
5))

scala> res0._1
res1: List[Int] = List(6, 7, 8, 9, 10)

scala> res0._2
res2: List[Int] = List(1, 2, 3, 4, 5)


scala> val numbers = List(1,2,3,4,5,6,7,8,9,10)
numbers: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

scala> numbers.find((i: Int) => i > 5)
res5: Option[Int] = Some(6)

scala> numbers.drop(5)
res0: List[Int] = List(6, 7, 8, 9, 10)

scala> numbers.dropWhile((i: Int) => i < 6)
res0: List[Int] = List(6, 7, 8, 9, 10)


scala> numbers.foldLeft(0)((m: Int, n: Int) => m + n)
res0: Int = 55

scala> numbers.foldLeft(0) { (m: Int, n: Int) => println("m: " + m +
" n: " + n); m + n }
m: 0 n: 1
m: 1 n: 2
m: 3 n: 3
m: 6 n: 4
m: 10 n: 5
m: 15 n: 6
m: 21 n: 7
m: 28 n: 8
m: 36 n: 9
m: 45 n: 10
res0: Int = 55


scala> numbers.foldRight(0)((m: Int, n: Int) => m + n)
res0: Int = 55

scala> numbers.foldRight(0)((m: Int, n: Int) => println("m: " + m + "
n: " + n); m + n)
m: 10 n: 0
m: 9 n: 10
m: 8 n: 19
m: 7 n: 27
m: 6 n: 34
m: 5 n: 40
m: 4 n: 45
m: 3 n: 49
m: 2 n: 52
m: 1 n: 54
res0: Int = 55


scala> List(List(1, 2), List(3, 4)).flatten

scala> val nestedNumbers = List(List(1, 2), List(3, 4))
nestedNumbers: List[List[Int]] = List(List(1, 2), List(3, 4))

scala> nestedNumbers.flatMap(x => x.map(_ * 2))


scala> val lista = List(p1, p2, p3)
lista: List[Pessoa] = List(Pessoa(Joao,83), Pessoa(Maria,78),
Pessoa(Isaias,33))

scala> lista.filter(pessoa => pessoa.idade > 70)
res2: List[Pessoa] = List(Pessoa(Joao,83), Pessoa(Maria,78))


Scalaz Combinator

scala> List(10, 20, 30) |@| List(1, 2, 3) apply (_ * _)

res0: List[Int] = List(10, 20, 30, 20, 40, 60, 30, 60, 90)


Conversões Java / Scala
import scala.collection.JavaConversions._

val sl = new scala.collection.mutable.ListBuffer[Int]
val jl : java.util.List[Int] = sl
val sl2 : scala.collection.mutable.Buffer[Int] = jl
assert(sl eq sl2)

Conversões Mão Dupla
scala.collection.Iterable <=> java.lang.Iterable
scala.collection.Iterable <=> java.util.Collection
scala.collection.Iterator <=> java.util.{ Iterator, Enumeration }
scala.collection.mutable.Buffer <=> java.util.List
scala.collection.mutable.Set <=> java.util.Set
scala.collection.mutable.Map <=> java.util.{ Map, Dictionary }
scala.collection.mutable.ConcurrentMap <=>
java.util.concurrent.ConcurrentMap


Conversões Java / Scala
Conversões Mão Única
scala.collection.Iterable <=> java.lang.Iterable
scala.collection.Iterable <=> java.util.Collection
scala.collection.Iterator <=> java.util.{ Iterator, Enumeration }
scala.collection.mutable.Buffer <=> java.util.List
scala.collection.mutable.Set <=> java.util.Set
scala.collection.mutable.Map <=> java.util.{ Map, Dictionary }
scala.collection.mutable.ConcurrentMap <=>
java.util.concurrent.ConcurrentMap

Scala – Actors

Scala Actors

 Abstração em processos Assíncronos

 Comunicação através de envio e recepção de
mensagens

 Tratamento de uma mensagem por vez

 Melhor utilizado em cenários que podem ser divididos
em várias etapas

Scala – Actors

Scala Actors
class Ping(count: Int, pong: Actor) extends Actor {
def act() {
var pingsLeft = count - 1
pong ! Ping
loop {
react {
case Pong =>
if (pingsLeft % 1000 == 0)
println("Ping: pong")
if (pingsLeft > 0) {
pong ! Ping
pingsLeft -= 1
} else {
println("Ping: stop")
pong ! Stop
exit()
}
}
}
}
}

Scala – Actors

Scala Actors
class Pong extends Actor {
def act() {
var pongCount = 0
loop {
react {
case Ping =>
if (pongCount % 1000 == 0)
println("Pong: ping "+pongCount)
sender ! Pong
pongCount += 1
case Stop =>
println("Pong: stop")
exit()
}
}
}
}

object pingpong extends Application {
val pong = new Pong
val ping = new Ping(100000, pong)
ping.start
pong.start
}

Scala – Actors

Akka Actors

Scala – Ferramentas de Teste

 ScalaTest (http://www.scalatest.org)
Test Driven Development (TDD)
 Behaviour-Driven Development (BDD)
 Funcional, integração e aceitação
import org.scalatest.FunSpec

class ExampleSpec extends FunSpec {

describe("A Stack") {

it("should pop values in last-in-first-out order") (pending)

it("should throw NoSuchElementException if an empty stack is
popped") (pending)
}
}

Scala – Ferramentas de Teste

 specs2 (http://etorreborre.github.com/specs2/)
 Testes unitários
 Testes de aceitação

import org.specs2.mutable._

class HelloWorldSpec extends Specification {

"The 'Hello world' string" should {
"contain 11 characters" in {
"Hello world" must have size(11)
}
"start with 'Hello'" in {
"Hello world" must startWith("Hello")
}
"end with 'world'" in {
"Hello world" must endWith("world")
}
}
}

Scala – IDEs

http://scala-ide.org/

http://www.jetbrains.com/idea/

Scala – Ferramentas de Build

 SBT (https://github.com/harrah/xsbt/wiki)

 MAVEN (http://maven.apache.org/)

Scala – Frameworks Web (Full)

Scala – Frameworks Web Java Compatíveis com Scala

Spring MVC V-Raptor

http://www.contasrefeitas.com.br/

Scala – Timeline Twitter

 Mais de 100 milhões de usuários ativos

 250 mil Tweets por dia
3 mil tweets / segundo – Média diária
5 mil tweets / segundo – Pico
Mais de 10 mil Tweets / segundo (Super Bowl)

 Poll-based
200 mil queries por segundo
Latência 1 milesegundo na média

 Buscas
30 mil queries por segundo

https://github.com/twitter/finagle

Obrigado
isaias.barroso@strategiatec.com.br
@isaias_barroso

Scala uma poderosa linguagem para a jvm

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