DR. SCALALOVE

Dianne MarshDirector of Engineering -- Cloud Tools, NetflixScalaBay Meetup, Sept 2013

OR HOW

I LEARNED

TO STOP

WORRYING AND

LOVE FUNCTIONS

Dr. Strangelove, 1964

“If this thing turns out to be half as important

as I think it will be, I think you’ll all be in

line for some personal citations and

promotions when this thing is over.”

What is Scala?

Object-oriented + FunctionalRuns on JVMBuild on Java expertise

Why Is it Scary?

Early adopters scared folks awayLost elasticity of learning new programming languagesComfort zone

What’s the Gain?

Modern language featuresLet compiler work for you!

REPL

Interactive InterpreterRead Evaluate Print Loop

Type Inference

val x = 5

val y = "Once upon a time"

val l = List("This", "is", "a", "List")

Methods

def squareIt(x: Int) = x*x

Anatomy of a Case Classcase class Camera(width: Int, height: Int) { def megapixels = (width * height)/1000000.0 def HD = megapixels > 1.08}

val camera = new Camera(1024, 768)camera.megapixels is 0.786432camera.HD is falsecamera is "Camera(1024,768)"

Reducing Boilerplate

class Dimension(var height:Int,

var width:Int)

val c = new Dimension(5,7)

c.height is 5

c.height = 10

c.height is 10

c.width = 19

c.width is 19

Pattern Matching

def batteryIndicator(batteryLevel: Int) =

batteryLevel match {

case l if (l > 60) => "GREEN"

case l if (l > 20) => "YELLOW"

case _ => "RED"

}

Traits

trait Digital {

def batteryIndicator(batteryLevel:

Int) = …}

val d = new Camera(1024, 768) with Digital

d.batteryIndicator(56) is "YELLOW"

Functions are Objects

val v = Vector(19, 1, 7, 3, 2, 14)

v.sorted is Vector(1, 2, 3, 7, 14, 19)

v.sortWith((i, j) => j < i) is

Vector(19, 14, 7, 3, 2, 1)

It’s OK

To use Scala as a Better Java

Reaching into Java

import org.apache.commons.math._import stat.regression.SimpleRegression val r = new SimpleRegressionr.addData(1, 1)r.addData(2, 1.1)r.addData(3, 0.9)r.addData(4, 1.2)r.getN is 4r.predict(6) is 1.19

It’s OK

To be verbose

Verbose Version

// Euler1.scala

val nums = 3 until 1000

val somenums = nums.filter

(x => (x % 3 == 0 || x % 5 ==0))

var sum = 0

somenums.foreach(sum += _)

Find the Sweet Spot

// Euler2.scala

val nums = 3 until 1000

val somenums = nums filter

(x => (x % 3 == 0 || x % 5 ==0))

val sum = somenums reduceLeft

{(x:Int,y:Int) => x + y}

More than 1 way ...

// Euler3.scala

val nums = 3 until 1000

val somenums = nums filter

(x => (x % 3 == 0 || x % 5 ==0))

val sum = somenums.foldLeft(0)(_+_)

Back off if it’s too much

// Euler4.scala

val nums = 3 until 1000

val somenums = nums filter

(x => (x % 3 == 0 || x % 5 ==0))

(0/:somenums)(_+_)

Code should be readable

To your teamTo your customersTo yourself, in 6 months

Killer Apps in Scala

Compute intensiveConcurrency

Reactive applications● Resilient● Scalable● Interactive, single-page● Event Driven

Learning

Scala Koans -- scalakoans.orgCase Studies at TypesafeBlogsBooks

Practicing

Solve Euler problemsUse ScalaTestUse for non-production code

Contact Info

@dmarshdmarsh@netflix.com

We are always hiring ...