#395 About Scala

An overview of the Scala programming language, its features, and ecosystem. Includes setting up and running on macOS.

Notes

Scala saw features in Bruce Tate’s Seven Languages in Seven Weeks.

Scala In a Nutshell

• Scala is a modern, statically typed programming language that runs on the JVM, designed to combine object-oriented and functional programming in a concise, expressive syntax.

• Scala has powerful language features such as type inference, immutability by default, pattern matching, higher-order functions, traits (for flexible composition), case classes, and seamless interoperability with Java and existing JVM libraries.

• Scala has a strong ecosystem, including build tools like sbt, popular frameworks and libraries such as Akka, Play, Cats, ZIO, and Spark (where Scala is the primary language), making it common in data engineering, distributed systems, and backend services.

• Scala has multiple runtime targets beyond the JVM, including Scala.js (JavaScript) and Scala Native, allowing shared code across server, browser, and native applications.

• Scala is governed by a combination of stewardship from Lightbend (the original creators), the Scala Center (which supports open-source development and education), and an open, community-driven language evolution process through Scala Improvement Proposals (SIPs).

• Scala has an active global community of developers, researchers, and companies, with strong ties to academia and industry, and a culture that emphasizes functional programming principles, type safety, and scalable system design.

Why Scala?

Why use Scala?

• Expressiveness without losing performance Scala lets you write very concise, high-level code (especially with functional patterns) while still compiling to fast JVM bytecode.

• Best of OO and functional programming You can model domains with objects and lean on functional techniques like immutability, pure functions, and algebraic data types—useful for complex, evolving systems.

• Strong static typing that scales Scala’s type system catches many errors at compile time without excessive verbosity, which pays off in large or long-lived codebases.

• First-class JVM interoperability You can use any Java library directly, migrate Java code incrementally, and deploy on mature JVM infrastructure (monitoring, profiling, cloud tooling).

• Excellent for concurrency and distributed systems Functional patterns plus libraries like Akka, ZIO, and Cats Effect make it easier to reason about concurrency, fault tolerance, and parallelism.

• Industry standard for big data Apache Spark is written in Scala and exposes its most natural API in Scala, making it a top choice for data engineering and analytics.

• Multi-platform reach With Scala.js and Scala Native, you can share core logic across backend, frontend, and native code.

• Good fit for complex domains When business rules, state transitions, or invariants are tricky, Scala’s pattern matching and type system help encode correctness directly in the code.

• Active ecosystem and serious users Backed by a strong open-source community and used in production by many tech and data-driven companies.

In short: use Scala when you want Java-level performance and ecosystem with much stronger abstraction, correctness, and expressiveness—especially for large, concurrent, or data-heavy systems.

Test drive: Scala on macOS

To install Scala, it is recommended to use cs setup, the Scala installer powered by Coursier. It ensures that a JVM and standard Scala tools are installed on your system.

I am running macOS on Apple Silicon,

$ brew install coursier && coursier setup
...
Found a JVM installed under /opt/homebrew/opt/openjdk/libexec/openjdk.jdk/Contents/Home.

Checking if ~/Library/Application Support/Coursier/bin is in PATH
  Should we add ~/Library/Application Support/Coursier/bin to your PATH via ~/.profile, ~/.bash_profile? [Y/n] Y

Checking if the standard Scala applications are installed
  Installed ammonite
  Installed cs
  Installed coursier
  Installed scala
  Installed scalac
  Installed scala-cli
  Installed sbt
  Installed sbtn
  Installed scalafmt

As I’m using a bash shell, I made sure the JDK and Coursier paths are set in .bash_profile:

export PATH="/opt/homebrew/opt/openjdk/bin:$PATH"
export PATH="$PATH:/Users/paulgallagher/Library/Application Support/Coursier/bin"

In a fresh terminal window, let’s verify the tools work.

OK, some unexpected warnings e.g.

$ scalac --version
WARNING: A terminally deprecated method in sun.misc.Unsafe has been called
WARNING: sun.misc.Unsafe::objectFieldOffset has been called by scala.runtime.LazyVals$ (file:/Users/paulgallagher/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala3-library_3/3.7.4/scala3-library_3-3.7.4.jar)
WARNING: Please consider reporting this to the maintainers of class scala.runtime.LazyVals$
WARNING: sun.misc.Unsafe::objectFieldOffset will be removed in a future release
Scala compiler version 3.7.4 -- Copyright 2002-2025, LAMP/EPFL

Apparently:

• it’s a JDK warning, not a Scala bug.
• Scala 3.7.4 uses sun.misc.Unsafe internally for lazy val.
• New Java versions now warn loudly about it.
• It’s safe for now, expected, and already on the Scala roadmap.

Ignoring the warnings:

$ scalac --version
Scala compiler version 3.7.4 -- Copyright 2002-2025, LAMP/EPFL
$ scala --version
Scala code runner version: 1.9.1
Scala version (default): 3.7.4
$ scala-cli --version
Scala CLI version: 1.11.0
Scala version (default): 3.7.4
$ amm --version
Ammonite REPL & Script-Runner, 3.0.6
$ scalafmt --version
scalafmt 3.10.3

Hello World

Following the Getting Started Guide..

The most basic scale program in hello.scala

//> using scala 3.7.4

@main
def hello(): Unit =
  println("Hello, World!")

Running it directly for the first time, scala downloaded the JVM and compilation server and compiled the program:

$ scala run hello.scala

Downloading JVM temurin:17
Downloading compilation server 2.0.13
Starting compilation server
Compiling project (Scala 3.7.4, JVM (17))
Compiled project (Scala 3.7.4, JVM (17))
Hello, World!

Re-running:

$ scala run hello.scala
Hello, World!

Credits and References

• https://www.scala-lang.org/
• https://www.scala-js.org/
• Seven Languages in Seven Weeks - Chapter 5: Scala