Scala runs...

  • on the JVM
  • on JavaScript in your browser
  • natively with LLVM beta

Scala in a Nutshell

click the boxes below to see Scala in action!

Seamless Java Interop

Scala runs on the JVM, so Java and Scala stacks can be freely mixed for totally seamless integration.

Type Inference

So the type system doesn’t feel so static. Don’t work for the type system. Let the type system work for you!

Concurrency & Distribution

Use data-parallel operations on collections, use actors for concurrency and distribution, or futures for asynchronous programming.

Author.scala
class Author(val firstName: String,
    val lastName: String) extends Comparable[Author] {

  override def compareTo(that: Author) = {
    val lastNameComp = this.lastName compareTo that.lastName
    if (lastNameComp != 0) lastNameComp
    else this.firstName compareTo that.firstName
  }
}

object Author {
  def loadAuthorsFromFile(file: java.io.File): List[Author] = ???
}
App.java
import static scala.collection.JavaConversions.asJavaCollection;

public class App {
    public List<Author> loadAuthorsFromFile(File file) {
        return new ArrayList<Author>(asJavaCollection(
            Author.loadAuthorsFromFile(file)));
    }

    public void sortAuthors(List<Author> authors) {
        Collections.sort(authors);
    }

    public void displaySortedAuthors(File file) {
        List<Author> authors = loadAuthorsFromFile(file);
        sortAuthors(authors);
        for (Author author : authors) {
            System.out.println(
                author.lastName() + ", " + author.firstName());
        }
    }
}

Combine Scala and Java seamlessly

Scala classes are ultimately JVM classes. You can create Java objects, call their methods and inherit from Java classes transparently from Scala. Similarly, Java code can reference Scala classes and objects.


In this example, the Scala class Author implements the Java interface Comparable<T> and works with Java Files. The Java code uses a method from the companion object Author, and accesses fields of the Author class. It also uses JavaConversions to convert between Scala collections and Java collections.

Type inference
scala> class Person(val name: String, val age: Int) {
     |   override def toString = s"$name ($age)"
     | }
defined class Person

scala> def underagePeopleNames(persons: List[Person]) = {
     |   for (person <- persons; if person.age < 18)
     |     yield person.name
     | }
underagePeopleNames: (persons: List[Person])List[String]

scala> def createRandomPeople() = {
     |   val names = List("Alice", "Bob", "Carol",
     |       "Dave", "Eve", "Frank")
     |   for (name <- names) yield {
     |     val age = (Random.nextGaussian()*8 + 20).toInt
     |     new Person(name, age)
     |   }
     | }
createRandomPeople: ()List[Person]

scala> val people = createRandomPeople()
people: List[Person] = List(Alice (16), Bob (16), Carol (19), Dave (18), Eve (26), Frank (11))

scala> underagePeopleNames(people)
res1: List[String] = List(Alice, Bob, Frank)

Let the compiler figure out the types for you

The Scala compiler is smart about static types. Most of the time, you need not tell it the types of your variables. Instead, its powerful type inference will figure them out for you.

In this interactive REPL session (Read-Eval-Print-Loop), we define a class and two functions. You can observe that the compiler infers the result types of the functions automatically, as well as all the intermediate values.

Concurrent/Distributed
val x = Future { someExpensiveComputation() }
val y = Future { someOtherExpensiveComputation() }
val z = for (a <- x; b <- y) yield a*b
for (c <- z) println("Result: " + c)
println("Meanwhile, the main thread goes on!")

Go Concurrent or Distributed with Futures & Promises

In Scala, futures and promises can be used to process data asynchronously, making it easier to parallelize or even distribute your application.

In this example, the Future{} construct evaluates its argument asynchronously, and returns a handle to the asynchronous result as a Future[Int]. For-comprehensions can be used to register new callbacks (to post new things to do) when the future is completed, i.e., when the computation is finished. And since all this is executed asynchronously, without blocking, the main program thread can continue doing other work in the meantime.

Traits

Combine the flexibility of Java-style interfaces with the power of classes. Think principled multiple-inheritance.

Pattern Matching

Think “switch” on steroids. Match against class hierarchies, sequences, and more.

Higher-order functions

Functions are first-class objects. Compose them with guaranteed type safety. Use them anywhere, pass them to anything.

Traits
abstract class Spacecraft {
  def engage(): Unit
}
trait CommandoBridge extends Spacecraft {
  def engage(): Unit = {
    for (_ <- 1 to 3)
      speedUp()
  }
  def speedUp(): Unit
}
trait PulseEngine extends Spacecraft {
  val maxPulse: Int
  var currentPulse: Int = 0
  def speedUp(): Unit = {
    if (currentPulse < maxPulse)
      currentPulse += 1
  }
}
class StarCruiser extends Spacecraft
                     with CommandoBridge
                     with PulseEngine {
  val maxPulse = 200
}

Flexibly Combine Interface & Behavior

In Scala, multiple traits can be mixed into a class to combine their interface and their behavior.

Here, a StarCruiser is a Spacecraft with a CommandoBridge that knows how to engage the ship (provided a means to speed up) and a PulseEngine that specifies how to speed up.

Switch on the structure of your data

In Scala, case classes are used to represent structural data types. They implicitly equip the class with meaningful toString, equals and hashCode methods, as well as the ability to be deconstructed with pattern matching.


In this example, we define a small set of case classes that represent binary trees of integers (the generic version is omitted for simplicity here). In inOrder, the match construct chooses the right branch, depending on the type of t, and at the same time deconstructs the arguments of a Node.

Pattern matching
// Define a set of case classes for representing binary trees.
sealed abstract class Tree
case class Node(elem: Int, left: Tree, right: Tree) extends Tree
case object Leaf extends Tree

// Return the in-order traversal sequence of a given tree.
def inOrder(t: Tree): List[Int] = t match {
  case Node(e, l, r) => inOrder(l) ::: List(e) ::: inOrder(r)
  case Leaf          => List()
}

Go Functional with Higher-Order Functions

In Scala, functions are values, and can be defined as anonymous functions with a concise syntax.

Scala
val people: Array[Person]

// Partition `people` into two arrays `minors` and `adults`.
// Use the anonymous function `(_.age < 18)` as a predicate for partitioning.
val (minors, adults) = people partition (_.age < 18)
Java
List<Person> people;

List<Person> minors = new ArrayList<Person>(people.size());
List<Person> adults = new ArrayList<Person>(people.size());
for (Person person : people) {
    if (person.getAge() < 18)
        minors.add(person);
    else
        adults.add(person);
}

Run Scala in your browser

Scastie is Scala + sbt in your browser! You can use any version of Scala, or even alternate backends such as Dotty, Scala.js, Scala Native, and Typelevel Scala. You can use any published library. You can save and share Scala programs/builds with anybody.

Run Scala code interactively

Online Courses

Functional Programming Principles in Scala

  • Free (optional paid certificate)
  • New sessions starting every 2 weeks!

Functional Program Design in Scala

  • Free (optional paid certificate)
  • New sessions starting every 2 weeks!

Parallel Programming

  • Free (optional paid certificate)
  • New sessions starting every 2 weeks!

Big Data Analysis with Scala and Spark

  • Free (optional paid certificate)
  • New sessions starting every 2 weeks!

Functional Programming in Scala Capstone

  • Free (optional paid certificate)
  • New sessions starting every 2 weeks!

Programming Reactive Systems

  • Free (optional paid certificate)
  • New sessions starting every 2 weeks!

Upcoming Training

Scala ecosystem

The Scala Library Index (or Scaladex) is a representation of a map of all published Scala libraries. With Scaladex, a developer can now query more than 175,000 releases of Scala libraries. Scaladex is officially supported by Scala Center.

The Scala Library Index

What’s New

BLOG

The Scala Center Action Towards a More Safe and Respectful Community Environment

Tuesday, May 11, 2021

The Scala community must be a safe and welcoming place for everyone. Therefore, the Scala Center condemns behaviors that may hurt our members or that are not in line with respect for our common values of equity, diversity and inclusion.

In our current society, these values are challenged every single day. We believe that it is very important to stand up for the ones that we believe in. This is why we take any report seriously, including those that have shaken our community in the last weeks.

This highlights the role that the Scala Center, in collaboration with everyone within the Scala community, must take to prevent and correct inappropriate behaviors, as well as any kind of harassment and discrimination.

A joint responsibility of stewardship

We are a worldwide community of people from very different social, cultural, ethnical, linguistic, religious and gender identity backgrounds, across all generations. This diversity is a core strength of our community, and to keep it we must lay down clear lines that should never be crossed.

The first framework is the Scala Code of Conduct (CoC), which we ask every person to acknowledge and follow to ensure a friendly, safe and welcoming environment for all.

Those who have a key role in or are the public face of our community stewardship, such as speakers, organizers, teachers, mentors, or program committee members, can have a huge impact on introducing and supporting these values, especially for newcomers.

We need everyone’s commitment to take care of our community by preventing any traumatic personal experience from happening, be it online or in person.

The Scala Center specific actions

We believe the most important thing is to offer to all of our members a safe and reliable way to report issues and decide how we are going to assess those cases and take action.

In that regard, and amongst others, we have identified that, in order to create truly safe spaces for anyone who engages in the Scala community, we must collaboratively establish:

  • A clear and well-defined governance model
  • A strong, well-defined reporting process
  • A permanent reporting commission
  • An official channel of communication for Scala event organizers and other Scala stewards to share and coordinate

Aiming to finalize by the end of 2021, we will start by:

  • Leading talks within the community on various levels to identify areas of improvement and map out the needs. We will start with a Scala Community Leaders Summit in June/July 2021.
  • Building stronger online and in-person policies, developing trainings, and provide resources to support stewards to implement the Scala CoC.
  • Proposing a safe and trustworthy reporting process and commission. In case members need help before any reporting process is implemented, they can already contact us at Scala-CoC@epfl.ch

Moreover, the Scala Center will actively support all the people who want to act as agents of change. If you are interested in sharing your practices and concerns, as well as participating in building safer spaces in our communities, please fill in this form.

We have faith that our community, standing united, will make all the necessary changes happen, and we thank everyone for welcoming this initiative.

The Scala Center team


Disclaimer (scope of the statement)

We recognize that events and issues that allegedly occurred at and around various Scala conferences are connected to larger social issues which touch many individuals and can be triggering.

For legal reasons, this statement does not:

  • mention specifics
  • refer to details of the alleged abusive behavior
  • link to external communication channels
  • pass judgment regarding the concrete case

The following statement does aim to:

  • express empathy and understanding
  • call for participation in creating a better community
  • propose immediate and long-term actions

The text in its entirety is created by the Scala Center organization, in consultation with the Scala Center advisory board and with the input of many community contributors who generously invested their free time to help us make it right.

Twitter Feed

See more tweets, or

Follow Scala on twitter

The Scala language is maintained by

  • Scala Center
  • Lightbend

Scala Center is supported by

EPFL Goldman Sachs 47 Degrees Twitter Spotify Lunatech VirtusLab Your company