scala — consolidated language guide — DedSec Project

Scala

Typical use: Functional programming.

Suggested file extension: .scala.

How to run / environment: Run with an installed Scala 3 toolchain.

Starter example

@main def hello(): Unit =
  def greet(name: String) = s"Hello, $name!"
  println(greet("Ada"))

How to read it

Expression-oriented style works alongside JVM libraries.

Common pitfall

Expression-oriented style works alongside JVM libraries.

Scala — Expanded practice workbook

Keep invalid text different from the number zero

Create a Scala 3 source file with a small total parser:

def parse(raw: String): Option[Int] =
  raw.toIntOption

@main def scoreDemo(): Unit =
  assert(parse("12") == Some(12))
  assert(parse("0") == Some(0))
  assert(parse("bad") == None)
  val values = List("3", "bad", "5")
  println(values.flatMap(parse).sum)

On a compatible Scala 3 launcher, the predicted printed sum is 8. The Option result tells the caller whether parsing succeeded. flatMap(parse) removes None values, which is convenient for an exploratory sum but could incorrectly suppress invalid production data. Record Scala version and launcher arguments because Scala 2 and Scala 3 entry-point syntax differ.

Preserve errors when dropping is unacceptable

Implement a stricter parser returning Either[String,Int]. Use Right for a valid integer and Left containing the rejected input for malformed text. Define what happens when a whole collection includes one error. Compare collecting every error with stopping at the first failure. Do not silently convert "bad" into zero.

Look at immutable collections

Run val original = List(1,2,3) and val updated = original.map(_ * 2). Verify original still contains the original values. In contrast to a mutable buffer, List.map creates a transformed collection without updating the existing list. Explain how this reduces accidental shared-state changes but does not prevent all concurrency bugs.

Independent exercise

Support whitespace around numeric strings using an explicit trim, then test " 12 ", the empty string, a negative number and values exceeding Int range. Add deterministic assertions; distinguish parser validity from a domain rule banning negatives. Documentation: https://docs.scala-lang.org/scala3/

Scala — Practical runnable code lab

How to run the samples

These independent samples use the appropriate language toolchain. Representative command: scala {file}. Replace placeholders with the actual filename, keep test data isolated, and do not interpret this as automatic installation.

Scala — Technical notes and common pitfalls

Core knowledge

1. The language supports object-oriented and functional abstractions.
2. Immutable collections can simplify concurrency and reasoning.
3. An effectful Future must be awaited or composed; launching it does not imply successful completion.