Scala Talk at FOSDEM 2009

A Scalable Language Martin Odersky FOSDEM 2009

The software landscape today … ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

This is both good and bad ,[object Object],[object Object],[object Object],[object Object],[object Object]

Alternative: Scalable languages ,[object Object],[object Object],[object Object],[object Object]

Scala is a scripting language ,[object Object],[object Object],[object Object],scala> var capital = Map("US"  "Washington", "France"  "Paris") capital: Map[String, String] = Map(US  Washington, France  Paris) scala> capital += ("Japan"  "Tokio") scala> capital("France") res7: String = Paris

Scala is the Java of the future ,[object Object],[object Object],[object Object],[object Object],object App { def main ( args : Array [ String ]) { if ( args exists (_. toLowerCase == "-help" )) printUsage () else process ( args ) } }

Interoperability ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Scala is a composition language ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],trait Analyzer { this : Backend => … } trait Backend extends Analyzer with Optimization with Generation { val global : Main import global ._ type OutputMedium <: Writable }

Is Scala a “kitchen-sink language”? ,[object Object],[object Object],[object Object],[object Object],[object Object]

Scala compared to Java Modeled in libraries: assert, enums, properties, events, actors, using, queries, … ,[object Object],+ abstract types Scala removes Scala adds - wildcards + existential types ,[object Object],+ pattern matching - special treatment of interfaces + mixin composition with traits - break, continue + closures - primitive types + operator overloading - static members + a pure object system

Scala cheat sheet (1): Definitions ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Scala cheat sheet (2): Expressions ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Scala cheat sheet (3): Objects and Classes ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Scala cheat sheet (4): Traits ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Spring Cleaning ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],var capital = Map ( "US" -> "Washington" , "Canada" -> "ottawa" ) capital += ( "Japan" -> "Tokyo" ) for (c <- capital.keys) capital(c) = capital(c).capitalize assert(capital( "Canada" ) == "Ottawa" )

… with one major difference ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Scalability demands extensibility ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Adding new datatypes - seamlessly ,[object Object],def factorial ( x : BigInt ): BigInt = if ( x == 0) 1 else x * factorial ( x - 1) Compare with using Java's class: import java.math.BigInteger def factorial ( x : BigInteger ): BigInteger = if ( x == BigInteger.ZERO) BigInteger . ONE else x . multiply (factorial(x.subtract(BigInteger.ONE))) }

Implementing new datatypes - seamlessly ,[object Object],import java.math.BigInteger class BigInt ( val bigInteger : BigInteger ) extends java . lang . Number { def + ( that : BigInt ) = new BigInt ( this . bigInteger add that . bigInteger ) def - ( that : BigInt ) = new BigInt ( this . bigInteger subtract that . bigInteger ) … // other methods implemented analogously } + is an identifier; can be used as a method name Infix operations are method calls: a + b is the same as a.+(b) a add b is the same as a.add(b)

Adding new control structures ,[object Object],[object Object],using ( new BufferedReader ( new FileReader ( path ))) { f => println ( f . readLine ()) } val f = new BufferedReader ( new FileReader ( path )) try { println ( f . readLine ()) } finally { if ( f != null ) f . close () }

Implementing new control structures: ,[object Object],def using [ T <: { def close () }] ( resource : T ) ( block : T => Unit ) { try { block ( resource ) } finally { if ( resource != null ) resource . close () } } T is a type parameter... … supporting a close method A closure that takes a T parameter

Break and continue ,[object Object],[object Object],[object Object],[object Object],[object Object],import scala.util.control.Breaks._ breakable { for (x <- elems) { println(x * 2) if (x > 0) break } }

Getting back break and continue

What makes Scala scalable? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Scala is object-oriented ,[object Object],[object Object],[object Object],scala> (1).hashCode res8: Int = 1 scala> (1).+(2) res10: Int = 3

Scala is functional ,[object Object],[object Object],[object Object],scala> val matrix = Array(Array(1, 0, 0), | Array(0, 1, 0), | Array(0, 0, 1)) matrix: Array[Array[Int]] = Array([I@164da25,… scala> matrix.exists(row => row.forall(0 ==)) res13: Boolean = false

Functions are objects ,[object Object],[object Object],[object Object],[object Object],[object Object],trait Function1 [ -S , +T ] { def apply ( x : S ): T } new Function1 [ Int , Int ] { def apply ( x : Int ) = x + 1 }

Why should I care? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Partial functions ,[object Object],[object Object],[object Object],[object Object],[object Object],trait PartialFunction [- A , + B ] extends ( A => B ) { def isDefinedAt ( x : A ): Boolean }

Developing new paradigms ,[object Object],[object Object],[object Object],[object Object]

Erlang-style actors ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],A pattern matching block of type PartialFunction[ MessageType , ActionType ]

A simple actor case class Data ( bytes : Array [ Byte ]) case class Sum ( receiver : Actor ) val checkSumCalculator = actor { var sum = 0 loop { receive { case Data ( bs ) => sum += hash ( bs ) case Sum ( receiver ) => receiver ! sum } } } } repeatedly receive messages Spawn a new actor

Implementing receive ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Other Approaches to Scalability ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Where are we now? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

The Scala community ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Tool support ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Who’s using it? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Learning Scala ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Thank You To try it out: scala-lang.org Thanks also to the (past and present) members of the Scala team: Philippe Altherr, Vincent Cremet, Iulian Dragos, Gilles Dubochet, Burak Emir, Sebastian Hack, Philipp Haller, Sean McDirmid, Ingo Meier, Adriaan Moors, Stéphane Micheloud, Nikolay Mihaylov, Anders Nielssen, Tiark Rompf, Lukas Rytz, Michel Schinz, Lex Spoon, Erik Stenman, Geoffrey Alan Washburn, Matthias Zenger .

Relationship between Scala and other languages ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Scala Talk at FOSDEM 2009

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Scala Talk at FOSDEM 2009