Scala cheat sheet

A scannable Scala reference: 8 short snippets across 5 topics, each linking back to the lesson it came from.

At a glance

Quick snippets

Setting up Scala 3: Coursier, Scala CLI and sbt

Coursier and the toolchain

# install Coursier, then the tools
curl -fL https://github.com/coursier/coursier/releases/latest/download/cs-x86_64-pc-linux.gz | gzip -d > cs
chmod +x cs && ./cs setup          # adds Coursier to PATH and installs the basics

cs install scala-cli sbt scalafmt
cs java --jvm temurin:21           # install and print the JAVA_HOME of a JDK
eval "$(cs java --env --jvm 21)"   # put that JDK on PATH for this shell

scala-cli version
sbt --version
scala --version

Coursier and the toolchain

//> using scala 3.5.0
//> using dep com.lihaoyi::os-lib:0.10.7
//> using test.dep org.scalameta::munit:1.0.0

import java.nio.file.Files

@main def demo(): Unit =
  val files = os.list(os.pwd).take(5)
  println(files.mkString(", "))

Coursier and the toolchain

scala-cli run demo.scala
scala-cli test .
scala-cli package . -o app --assembly     # a runnable fat jar
scala-cli repl

Full lesson: Setting up Scala 3: Coursier, Scala CLI and sbt →

Option, Either and functional error handling

Either for failure with a reason

import scala.util.{Try, Success, Failure}

// wrap a throwing call once, at the boundary
val parsed: Try[Int] = Try("not a number".toInt)

parsed match
  case Success(v) => println(v)
  case Failure(e) => println(s"failed: ${e.getMessage}")

// Either and Try agree on for-comprehensions, so they compose
def readPort(s: String): Either[String, Int] =
  Try(s.toInt).toEither.left.map(_ => s"'$s' is not a number").filterOrElse(_ > 0, "port must be positive")

Full lesson: Option, Either and functional error handling →

Givens, implicits and type classes

A type class end to end

// overriding an instance in a specific scope, for a test or a special case
object TestScope:
  given testEncoder: Encoder[Int] with
    def encode(a: Int) = "REDACTED"

  def render: String =
    import Encoder.encode
    encode(42)                      // picks the local given, which wins over the companion

Full lesson: Givens, implicits and type classes →

Testing with ScalaTest and MUnit

Property-based testing with ScalaCheck

// run inside sbt
//   testOnly com.example.CodecProperties
//   testOnly * -- -z "decode"
// Scala CLI
//   scala-cli test .
//   scala-cli test . --test-only com.example.CodecProperties

Full lesson: Testing with ScalaTest and MUnit →

sbt, dependencies and project structure

Cross-building and publishing

// cross-build for both Scala lines
ThisBuild / crossScalaVersions := Seq("3.5.0", "2.13.14")

// publish to a company repository
publishTo := Some("Company" at "https://repo.example.com/maven-releases")
credentials += Credentials(Path.userHome / ".sbt" / ".credentials")

// a library that must not ship test sources
Compile / packageBin / packageOptions +=
  Package.ManifestAttributes("Implementation-Version" -> version.value)

Cross-building and publishing

sbt +compile          # compile for every crossScalaVersions entry
sbt +publishLocal     # install into the local Ivy repository
sbt evicted           # show which dependency version won and why
sbt dependencyTree    # the full resolution graph
sbt ";clean;test"     # several commands in one invocation

Full lesson: sbt, dependencies and project structure →

FAQ

Related cheat sheets

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Last refreshed 2026-09-27.