eBay Inc. confidential

Peter Maas

2011-Q2

What it is and why it rocks

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Goals

• You’ll learn the what & why of Scala

• You’ll learn what basic Scala programs look like

• You’ll get an insight in how deep Scala can be

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Peter Maas

• Technical team lead at eBay Classifieds group working at Marktplaats.

• Interested in programming languages in general; every new concept you learn might help you solve problems in a smarter / cleaner way.

• Hasn’t worked on a MS Windows machine for quite a while.

• Background in Sound & Music, specialized in pattern recognition. But spend the last decade on web development.

• Might know me from: – Marktplaats.nl (admarkt)– VPRO (3voor12, cinema.nl, …)– Kennis- SURFnet (Video portals, Wikiwijs, Leraar24)– DBGA (Erfpacht register)– RaboBank (RaboMobiel)– Ruby, Clojure, Devnology or DuSe usergroups

• Proud dad of two beautiful kids.

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Scala

• Scalable Language

• Statically typed

• First class citizen on the JVM

• Multi paradigm: OO, FP

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Who uses it

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Basic features

Immutable value:

val name:Type = …

Mutable value:

var name:Type = …

A function:

def functionName(argName:argType):returnType = /* functionBody */

Class

class ClassName(constructorArg:argType) { }

Object:

object ObjectName { }

Tuple

(1,2) or (1,2,"booh",4,5) /* access t._1 , t._3 etc. */

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Basic control flow

If:

if(x < 5) doA else doB

For:

for(x <- 0 to 5) println(x)

for(x <- 0 to 5) yield(x * 2) /* returns collections containing x*2 vals */

for(x <- 0 to 5; y <- 0 to x) yield(x * y) /* comprehensions */

Pattern Matching:

something match {

case a:Int => println(a)

case (a:Int, b:String) =>

case x :: xs => /* head, tail */

case _ =>

}

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(Case) Classes

Java:public class Person {

public final String name;

public final int age;

Person(String name, int age) {

this.name = name;

this.age = age;

}

// TODO: implement equals

// TODO: implement hashCode

}

Scala:

case class Person(val name:String, val age:Int)

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Collections :: Immutable

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Collections :: Mutable

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Collections :: Operations

Traversing

list.foreach( it => println(it) )

list.foreach( println(_) )

Transforming

list.map( _ * 2)

urls.par.map(io.Source.fromURL(_).mkString(""))

Reducing / Folding

list.reduceLeft(_+_) /* f(f(f(a,b),c),d), f = + */

list.foldLeft(5)(_+_) /* f(f(f(f(5,a),b),c),d), f = + */

list.foldRight(List[Int]())((i,l) => if(i%2 == 0) i :: l else l )

Filtering

list.filterNot(_%2 == 0)

Sorting

list.sorted, list.sortBy(it => it.name)

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Collections :: Operations

Grouping

(1 to 10).groupBy(v => v%5) /* Map[Int, Vector[Int]] */

Zip

List(1,2,3,4).zip(List(5,6,7,8)) /* List((1,5), (2,6), (3,7), (4,8)) */

Much more:

diff, distinct, exists, grouped, intersect, slice

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More concepts

• Case classes

• Structural Typing

• Traits

• Implicit conversions

• Operators are functions

• Actors

• Laziness / Streams

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Structural typing

Statically typed version of duck typing

Immutable value:

def feed(anyThing: { def eat(f:Food):Unit }) = {

anyThing.eat(myFood)

}

Keeps coupling as low as possible.

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Actors

• Scalas’ main construct for parallelizing tasks

• Actors are concurrent processes that communicate by exchanging messages

• Akka!

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Frameworks

• All existing Java frameworks

• Database– Querulous– Casbah

• Web– Play! Scala module– Lift

• Messaging– Kafka– Kestrel

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Note on tools

• During this presentations you’ve seen SBT, VIM and Intellij Idea in action

• All major (Java) build systems include support (Maven, Ant, Grails, Buildr, SBT)

• Scala IDE (Eclipse based, maintained by TypeSafe)

• Scala plugin for Intellij IDEA

• Scala plugin for NetBeans

And yes… it’s not 100% on par with tooling Java people are generally used to; but still good enough to work in a comfortable way.

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More info

• http://scala-lang.org

• Programming in Scala 2nd edition (Odersky)

• twitter.com/p3t0r

• log4p.com

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Q&A (YES: WE ARE HIRING)

One more thing: