Scala Rules

Version: Scala 3.4+

Tooling

• Build: sbt or Mill
• Testing: ScalaTest or munit
• Formatting: scalafmt
• Linting: scalafix, WartRemover

Best Practices (2026)

• Prefer immutability and pure functions
• Use case classes for data modeling
• Use ZIO 2.x or Cats Effect 3.x for effect systems
• Use Iron for compile-time type refinement
• Use Tapir for type-safe HTTP APIs

ZIO Patterns

// ZIO service pattern
trait UserService:
  def getUser(id: UserId): Task[User]

object UserService:
  def getUser(id: UserId): ZIO[UserService, Throwable, User] =
    ZIO.serviceWithZIO[UserService](_.getUser(id))

// ZLayer for dependency injection
val live: ZLayer[Database, Nothing, UserService] =
  ZLayer.fromFunction(UserServiceLive(_))

Iron Type Refinement

import io.github.iltotore.iron.*
import io.github.iltotore.iron.constraint.numeric.*

// Compile-time validated types
type Age = Int :| Positive
type Email = String :| Match["^[\\w-\\.]+@([\\w-]+\\.)+[\\w-]{2,4}$"]

def createUser(name: String, age: Age): User = ???

Spark Patterns

• Use Dataset over RDD for type safety
• Use Catalyst optimizer hints
• Partition data appropriately
• Cache intermediate results

MoAI Integration

• Use Skill("moai-lang-scala") for detailed patterns
• Follow TRUST 5 quality gates