Scala

roadmap.sh: https://roadmap.sh/scala

Suggested path through the Scala nodes. Each node links to its lesson when written.

Nodes

Getting started

• What is Scala
• Scala 2 vs Scala 3
• Installing the JDK
• sbt build tool
• Scala CLI
• REPL / worksheets
• IDE & Metals setup

Basics & syntax

• Values & variables (val/var)
• Basic data types
• Operators
• String interpolation
• Expressions vs statements
• Conditionals (if/else)
• Loops & ranges
• Comments & scaladoc

Functions

• Defining methods
• Function literals & lambdas
• Higher-order functions
• Default & named arguments
• Variadic parameters
• Currying & partial application
• Tail recursion
• By-name parameters

Object-oriented Scala

• Classes & constructors
• Objects & companion objects
• Case classes
• Traits
• Abstract classes
• Access modifiers
• Inheritance & overriding
• Sealed traits
• Enums (Scala 3)

Functional programming

• Immutability
• Pure functions & referential transparency
• Pattern matching
• Option, Some, None
• Either & Try
• for-comprehensions
• Recursion over iteration
• Algebraic data types

Collections

• List, Vector, Seq
• Set & Map
• Tuples
• Arrays
• map / flatMap / filter
• fold & reduce
• Lazy collections (LazyList)
• Immutable vs mutable collections

Type system

• Type inference
• Generics & type parameters
• Variance (covariance/contravariance)
• Bounds (upper/lower)
• Implicits / given & using (Scala 3)
• Type classes
• Context bounds
• Higher-kinded types
• Opaque types (Scala 3)
• Union & intersection types (Scala 3)

Concurrency & async

• Futures & Promises
• ExecutionContext
• Parallel collections
• Akka / Pekko actors
• Cats Effect
• ZIO

Error handling

• Exceptions vs functional errors
• Try / Success / Failure
• Validated & error accumulation

Ecosystem & libraries

• Cats
• ZIO
• Akka / Pekko
• Play Framework
• http4s
• Spark (big data)
• Circe (JSON)
• Doobie (database)

Tooling

• sbt tasks & plugins
• Mill build tool
• Scalafmt
• Scalafix
• Dependency management

Testing

• ScalaTest
• munit
• ScalaCheck (property-based)
• Mockito for Scala

Build & deploy

• Packaging & assembly (fat jars)
• Cross-compilation
• Scala.js
• Scala Native
• Publishing libraries

Resources

See resources.md.

Project ideas

• Build a typed JSON REST API with http4s + Circe and run it on Cats Effect.
• Write a property-based-tested parser/calculator using pattern matching and ADTs.
• Process a dataset with Apache Spark, modeling the pipeline with case classes and for-comprehensions.