Six years of Scala and counting

7 years of Scalaand countingScala Days Vienna 2017

Scala Vienna May 2016 - manuel.bernhardt.io - @elmanu

6 years of Scalaand countingScala Vienna User Group May 2016


Agenda1. Quick introduction to Scala

2. Learning Scala

3. Using Scala

4. Learnings, reflection, observations, impressions

5. Questions


Manuel Bernhardt

• I help companies getting started with using reactive applications in their distributed systems infrastructure

• http://manuel.bernhardt.io


Scala: an introduction


Scala introduction

• first version released in 2003

• Martin Oderksy, EPFL

• an estimated more than half a million Scala developers 1

1 http://www.scala-lang.org/blog/2016/03/14/announcing-the-scala-center.html


Scala Center

• non-for-profit foundation for Scala education and community guidance

• established at EPFL

• founding members: IBM, verizon, Goldman Sachs, nitro, Lightbend


Favourite Feature tour


case classespublic class User {

private final String name; private final String surname; private final Integer age;

public User(String name, String surname, Integer age) { this.name = name; this.surname = surname; this.age = age; }

public String getName() { return this.name; }

public String getSurname() { return this.surname; }

public String getAge() { return this.age; }

@Override public int hashCode() { // ... }

@Override public boolean equals(Object that) { // ... }}


case classescase class User(name: String, surname: String, age: Int)


case classescase class User(name: String, surname: String, age: Int)

val bob = User("Bob", "Marley", 42)

val namedBob = User(name = "Bob", surname = "Marley", age = 22)

val john = bob.copy(name = "John")


case class• perfect example of the terseness Scala provides

• hashcode, equals, toString for free

• serializable by default


type inferenceval foo = "Bar" // foo: String = Bar

val answer = 42 // answer: Int = 42

val price = 9.99 // price: Double = 9.99

val nums = List(1, 2, 3) // nums: List[Int] = List(1, 2, 3)

val map = Map("abc" -> List(1, 2, 3))// map: scala.collection.immutable.Map[String,List[Int]] = Map(abc -> List(1, 2, 3))


functions and higher-order functionsdef isMajor(user: User): Boolean = user.age > 18



class UserGroup { def filter(predicate: User ⇒ Boolean): List[User] = ...}



class UserGroup { def filter(predicate: User ⇒ Boolean): List[User] = ...}

userGroup.filter(isMajor) // returns only majors


Learning Scala


How "learnable" is Scala?

• Shadaj Laddad

• http://shadaj.me

• learned Scala at age 11-12

• talks at Scala Days, OSCON since 2012


How "learnable" is Scala?

• Coursera courses, 400.000+ participants - highest completation rate in the industry (10%, which is high for a MOOC 2)

• Scala as beginner programming language at Lund University of Technology 3

3 https://www.lth.se/english/about-lth/news/news/article/scala-will-be-the-beginner-programming-language-of/

2 Massive Open Online Course


My learning path

• 2010: started dabbling with Scala (books, using it in tests, small projects)

• 2011: discovering Functional Programming through Javascript. Using Play Framework 1 with the Scala module in my 2nd startup

• 2012: first large codebase to migration from Play 1 to Play 2.0.0 (based entirely on Scala)


My learning path• 2013: several client projects using Scala

• 2014-2016: architecture, prototyping, design, implementation, review of various production systems with Scala, Akka, Play Framework; writing Reactive Web Applications


My learning path• estimated 6 months to "click"

• imperative ⇒ declarative

• mutable, global state ⇒ immutable, expression-oriented

• longer to grasp or use more advanced concepts

• and how not to shoot myself in the foot with them


Your learning path?• new Coursera courses by the Scala Center

• https://scala.epfl.ch

• try to use Scala for something "real"

• and even if it is just tests in a real project


Using ScalaScala Vienna May 2016 - manuel.bernhardt.io - @elmanu

6 years without one of those pesky NullPointerException-s


Significantly less problems at runtime

• Scala compiler spots a whole plethora of problems at compile-time

• leveraged by e.g. Play Framework, high emphasis on "compiling everything"

• URLs

• Javascript (Google Clojure Scala Vienna May 2016 - manuel.bernhardt.io - @elmanu

Less code yieldshigher maintainbility

(Less is more)


IDE / Editors• IntelliJ IDEA

• Scala IDE for Eclipse

• ENSIME 5

• emacs, Atom, Sublime Text, vim

5 Enhanced Scala and java Interaction Mode for text Editors


Compiler• slower than the Java compiler

• but not a problem (anymore) on modern hardware

• especially with incremental compilation

• unless you deep dive into type-level and generic programming (e.g. shapeless library)

• much more precise than the Java compiler (type-safe ++)


Jobs & Developers


http://appliedscala.com/blog/2016/scala-popularity/Scala Vienna May 2016 - manuel.bernhardt.io - @elmanu

What I've learnedReflection, Impressions, (Advice)


The Dreyfus model of skill acquisition


Learning #1Spend a little time understanding

the language design


Understand Scala's essenceand your life will be easier


Learning #2Understand the purpose of the

language features


Scala has quite a few language featuresbecause it was designed to be extensible


Don't be that kid


Scala language levels 4

• Level A1: Beginning application programmer

• Level A2: Intermediate application programmer

• Level A3: Expert application programmer

4 http://www.scala-lang.org/old/node/8610


Scala language levels 4

• Level L1: Junior library designer

• Level L2: Senior library designer

• Level L3: Expert library designer

4 http://www.scala-lang.org/old/node/8610


The features you need to build

applicationsare not the sameas the ones you need to build

librariesScala Vienna May 2016 - manuel.bernhardt.io - @elmanu

SIP 18: Modularizing language featuresimport scala.language.implicitConversionsimport scala.language.dynamicsimport scala.language.postfixOpsimport scala.language.reflectiveCallsimport scala.language.higherKindsimport scala.language.existentialsimport scala.language.macros


Incidental complexityIs this really a problemspecific to Scala?Scala Vienna May 2016 - manuel.bernhardt.io - @elmanu

@SuppressWarnings({"unchecked", "rawtypes"})@Deprecated@OneToMany(@HowManyDBADoYouNeedToChangeALightBulb)@OneToManyMore @AnyOne @AnyBody@YouDoNotTalkAboutOneToMany // Fightclub, LOL@TweakThisWithThat( tweak = { @TweakID(name = "id", preferredValue = 1839), @TweakID(name = "test", preferredValue = 839), @TweakID(name = "test.old", preferredValue = 34), }, inCaseOf = { @ConditionalXMLFiltering(run = 5), })@ManyToMany @Many @AnnotationsTotallyRock @DeclarativeProgrammingRules @NoMoreExplicitAlgorithms@Fetch @FetchMany @FetchWithDiscriminator(name = "no_name")@SeveralAndThenNothing @MaybeThisDoesSomething@JoinTable(joinColumns = { @JoinColumn(name = "customer_id", referencedColumnName = "id")})@DoesThisEvenMeanAnything @DoesAnyoneEvenReadThis@PrefetchJoinWithDiscriminator @JustTrollingYouKnow @LOL@IfJoiningAvoidHashJoins @ButUseHashJoinsWhenMoreThan(records = 1000)@XmlDataTransformable @SpringPrefechAdapterprivate Collection employees; // http://annotatiomania.com


Learning #3Don't forget all about Object

Oriented Programming


class SynchronizationService {

private[services] def synchronizeTeeTimes( suite: Suite, dataType: SuiteDataType, eventuallyByteStream: Future[Enumerator[Array[Byte]]], removeDocsWithOlderTimestamps: Boolean): Future[Int] = ...

private[services] def synchronizeTournaments( suite: Suite, dataType: SuiteDataType, eventuallyByteStream: Future[Enumerator[Array[Byte]]], removeDocsWithOlderTimestamps: Boolean): Future[Int] = ...

}


class SynchronizationService {

private def synchronizeGolf[T, S](suite: Suite, dataType: SuiteDataType, eventuallyByteStream: Future[Enumerator[Array[Byte]]], toIndexDocuments: (Suite, Issuer, GolfClub) => Seq[T] => Iterable[S], // function! indexDocuments: Iterable[S] => Future[Boolean], // function! countDocuments: CountRequest => Future[Long], // function! verify: (Int, Long) => Unit, // function! removeDocsWithOlderTimestamps: Boolean)(implicit format: Format[T]): Future[Int] = ...

}


Learning #4Don't use every feature as a

hammer


for comprehensionval bobUser: Option[User] = ...val carlUser: Option[User] = ...

val bobCarlAge: Option[Int] = for { bob <- bobUser carl <- carlUser } yield bob.age + carl.age


for comprehension from hellfor { stopWatch <- Future.successful(startedStopWatch) startTimestampOfSync = DateTime.now() byteStream <- eventuallyByteStream suiteDocStream = toDocumentStream[T](byteStream) chunkedStream = suiteDocStream &> ExtraEnumeratees.chunker(ChunkSize) indexerSuccessStream = chunkedStream &> indexer indexerSuccess <- indexerSuccessStream.run(Iteratee.fold(true)(_ && _)) _ <- if (removedDocsWithOlderTimestamps) waitForElasticSearchToFinishIndexing().map(_ => removeDocsUpsertedBefore(issuer, dataType, startTimestampOfSync)) else Future.successful(()) count <- waitForElasticSearchToFinishIndexing().flatMap { _ => verifyCount(issuer, counter.get(), countDocuments, verify) }} yield { if (!indexerSuccess) error(s"Failed to index $dataType for ${suite.url}") val duration = scala.concurrent.duration.Duration(stopWatch.getNanoTime, TimeUnit.NANOSECONDS).toSeconds info(s"Done synchronizing ${counter.get()} $dataType for ${suite.url}, it took $duration s") count}


Learning #5Transitioning to Scala

(for teams)


Don't start a Scala projectwith a team comprised

of novice and advanced beginners


Don't start a <XYZ> projectwith a team comprised

of novice and advanced beginners


It's all about peopleThe biggest challenges of transitioning to Scala — or anything new — are rarely technical. Talented programmers can learn a new syntax, new concepts, and a new IDE. Rather, change often brings out the weaknesses in other areas like process and culture. 6— Kevin Webber

6 https://medium.com/@kvnwbbr/transitioning-to-scala-d1818f25b2b7#.x1tcfcs58


Building up Scala knowledge in your team• culture that emphasizes learning, create time for learning

• code reviews, discussions

• try to get one "Competent" on your team

• even if it's a "hired gun" helping to bootstrap & ensure best practices (& avoiding pitfalls)

• invest in training (Fast track to Scala, etc.)Scala Vienna May 2016 - manuel.bernhardt.io - @elmanu

Conclusion


Conclusioncase class User(name: String, surname: String, age: Int)



embrace Scala's terseness



embrace Scala's terseness

don't forget about the language levels


Thank you!Questions & Comments ?

• http://manuel.bernhardt.io

• @elmanu


Six years of Scala and counting

Engineering

Transcript of Six years of Scala and counting