Scala 3.4+ Development Specialist

Functional programming, effect systems, and big data processing for JVM applications.

Quick Reference

Auto-Triggers: Scala files (.scala, .sc), build files (build.sbt, project/build.properties)

Core Capabilities:

• Scala 3.4: Given/using, extension methods, enums, opaque types, match types
• Akka 2.9: Typed actors, streams, clustering, persistence
• Cats Effect 3.5: Pure FP runtime, fibers, concurrent structures
• ZIO 2.1: Effect system, layers, streaming, error handling
• Apache Spark 3.5: DataFrame API, SQL, structured streaming

Key Ecosystem Libraries:

• HTTP: Http4s 0.24, Tapir 1.10
• JSON: Circe 0.15, ZIO JSON 0.6
• Database: Doobie 1.0, Slick 3.5, Quill 4.8
• Streaming: FS2 3.10, ZIO Streams 2.1
• Testing: ScalaTest, Specs2, MUnit, Weaver

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Module Index

This skill uses progressive disclosure with specialized modules:

Core Language

• functional-programming.md - Scala 3.4 features: Given/Using, Type Classes, Enums, Opaque Types, Extension Methods

Effect Systems

• cats-effect.md - Cats Effect 3.5: IO monad, Resources, Fibers, FS2 Streaming
• zio-patterns.md - ZIO 2.1: Effects, Layers, ZIO Streams, Error handling

Frameworks

• akka-actors.md - Akka Typed Actors 2.9: Actors, Streams, Clustering patterns
• spark-data.md - Apache Spark 3.5: DataFrame API, SQL, Structured Streaming

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Implementation Guide

Project Setup (SBT 1.10)

In build.sbt, set ThisBuild / scalaVersion to "3.4.2" and organization. Define lazy val root project with settings including name and libraryDependencies. Add dependencies for cats-effect, zio, akka-actor-typed, http4s-ember-server, circe-generic, and scalatest for test scope. Include scalacOptions for deprecation, feature warnings, and Xfatal-warnings.

Quick Examples

Extension Methods: Use extension keyword with parameter in parentheses. Define methods like words splitting on whitespace and truncate checking length before taking characters and appending ellipsis.

Given and Using: Define trait with abstract method signature. Create given instance with with keyword and implement the method. Create functions with using parameter clause for implicit resolution.

Enum Types: Define enum with generic type parameters and plus variance annotations. Create case entries with parameters. Define methods on enum using match expression to handle each case, returning appropriate results.

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Context7 Integration

Library mappings for latest documentation:

Core Scala:

• /scala/scala3 - Scala 3.4 language reference
• /scala/scala-library - Standard library

Effect Systems:

• /typelevel/cats-effect - Cats Effect 3.5 documentation
• /typelevel/cats - Cats 2.10 functional abstractions
• /zio/zio - ZIO 2.1 documentation
• /zio/zio-streams - ZIO Streams 2.1

Akka Ecosystem:

• /akka/akka - Akka 2.9 typed actors and streams
• /akka/akka-http - Akka HTTP REST APIs
• /akka/alpakka - Akka connectors

HTTP and Web:

• /http4s/http4s - Functional HTTP server/client
• /softwaremill/tapir - API-first design

Big Data:

• /apache/spark - Spark 3.5 DataFrame and SQL
• /apache/flink - Flink 1.19 streaming
• /apache/kafka - Kafka clients 3.7

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Testing Quick Reference

ScalaTest: Extend AnyFlatSpec with Matchers. Use string description with should in for behavior. Make assertions with shouldBe for equality checks.

MUnit with Cats Effect: Extend CatsEffectSuite. Define test with string name. Return IO containing assertEquals assertions.

ZIO Test: Extend ZIOSpecDefault. Define spec as suite with test entries. Use for-comprehension to run effects and yield assertTrue assertions.

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Troubleshooting

Common Issues:

• Implicit resolution: Use scalac -explain for detailed error messages
• Type inference: Add explicit type annotations when inference fails
• SBT slow compilation: Enable Global / concurrentRestrictions in build.sbt

Effect System Issues:

• Cats Effect: Check for missing import cats.effect._ or import cats.syntax.all._
• ZIO: Verify layer composition with ZIO.serviceWith and ZIO.serviceWithZIO
• Akka: Review actor hierarchy and supervision strategies

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Works Well With

• moai-lang-java - JVM interoperability, Spring Boot integration
• moai-domain-backend - REST API, GraphQL, microservices patterns
• moai-domain-database - Doobie, Slick, database patterns
• moai-workflow-testing - ScalaTest, MUnit, property-based testing

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Additional Resources

For comprehensive reference materials:

• reference.md - Complete Scala 3.4 coverage, Context7 mappings, performance
• examples.md - Production-ready code: Http4s, Akka, Spark patterns

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Last Updated: 2026-01-11
Status: Production Ready (v2.1.0)