Ett första steg i Scala.

ScalaLand is a small fantasy role-playing domain — creatures with strength/wisdom/charisma, races (Elf, Dwarf), professions (Warrior, Wizard, Thief) and magical items — that the book reimplements chapter by chapter. Each com.programmera.scalaland* package is one chapter's take on the same model: first with plain classes, then traits and mixin composition, then immutability, functional style, and generics. The Scala 3 sibling packages redo four chapters with modern idioms (enum, trait parameters, opaque type, given/using) so old and new can be read side by side.

The trait chapter's model is the heart of the book. A race and a profession are mixed in at instantiation time — an Avatar without a race fails on construction:

val bilbo = new Avatar("Bilbo") with Elf with Thief   // ok
Avatar("RogueWithoutRace")                            // IllegalArgumentException

classDiagram
    direction TB

    class Creature {
        <<trait>>
        +name: String*
        +strength: Int
        +wisdom: Int
        +charisma: Int
        +hitpoints: Int
        #generateCreatureFeatures()
        +toString() String
    }

    class Elf {
        <<trait>>
        #generateCreatureFeatures()
    }
    class Dwarf {
        <<trait>>
        #generateCreatureFeatures()
    }

    class Professional {
        <<trait>>
        +climb() Int
        +magicAttack(foe) Unit
        +weaponAttack(foe) Unit
        #sufferDamage(foe, damage)
    }

    class Warrior {
        <<trait>>
        +climb() Int
        +weaponAttack(foe) Unit
    }
    class Wizard {
        <<trait>>
        +magicAttack(foe) Unit
    }
    class Thief {
        <<trait>>
        +climb() Int
    }

    class Avatar {
        <<case class>>
        +name: String
        +items: MagicalItemList
    }

    class MagicalItemList
    class DeathException

    Creature <|-- Elf : race
    Creature <|-- Dwarf : race
    Creature <|-- Professional
    Professional <|-- Warrior : profession
    Professional <|-- Wizard : profession
    Professional <|-- Thief : profession
    Professional <|-- Avatar
    Avatar o-- MagicalItemList : items
    Creature ..> DeathException : hitpoints = 0

Creature holds the mutable stats and throws DeathException when hitpoints reach zero; the race traits override stat generation, the profession traits override combat and climbing, and Avatar adds magical items whose modifiers stack on top of the base stats. The DieRoll, MagicalItem* and CreatureFeature helpers are re-exported from earlier chapters via the package object.

The repository is in the final phase of a Scala 2.8 → Scala 3 migration. See MIGRATION_TO_SCALA3.md for the full plan and per-phase commit log.

sbt compile                             # compile all sources
sbt testFull                            # run all smoke tests
sbt "scalafmtCheckAll; scalafmtSbtCheck" # check formatting
sbt "scalafixAll --check"               # check lint rules

Note (sbt 2): plain sbt test is incremental and may run zero tests on an up-to-date build — use testFull for the whole suite. Multiple commands on one invocation must be quoted and separated by ;.

The first sbt invocation will fetch Scala 3.3.8, ScalaTest 3.2.20 and the scalafix/scalafmt plugins.

The classic chapters from the book, kept as a working reference under Scala 3:

src/main/scala/com/programmera/
  scalaland1, scalaland1a, scalaland2, scalaland3, scalaland4   # class chapter
  scalaland_trait                                                # trait/mixin chapter
  scalaland_immutable1, _immutable2, _immutable3                 # objfunc chapter
  scalaland_func_final                                           # func chapter
  scalaland_generic                                              # generics chapter

A few of these (e.g. scalaland_immutable1.Npc, scalaland_immutable2.Npc) are deliberately marked "Incorrect" in their source comments — pedagogical anti-patterns the book uses to contrast against the cleaner alternatives.

New packages introduced during the migration to demonstrate Scala 3 idioms against their Scala 2 originals:

The legacy chapters and the _scala3_* siblings are intended to be read side by side — the contrast is the lesson.

The book itself lives at https://github.com/oluies/ScalaBook in DocBook 5 XML. Clone it as a sibling of this repo:

cd ~/projects && git clone https://github.com/oluies/ScalaBook.git

Tooling under .claude/skills/docbook/ and (forthcoming) scripts/book/ reaches ../ScalaBook by relative path. The two repos stay independent — code lands here, prose lands in ScalaBook.