02-recap-scala2-akka-typed-scala3.md

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Recap

Scala 2, Dotty, Scala 3, and Akka Typed

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Scala 2 - The current state

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• Currently supported versions
  • 2.12
  • 2.13
    • Important progress on compiler performance and collections rewrite
    • New, binary compatible Vector implementation
    • Most recent release 2.13.11
    • Allow, under some restrictions to use Scala 3 libraries in Scala 2 code (using Tasty) and vice-versa. See the Compatibility Reference pages in the Scala 3 Migration Guide

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Dotty/Scala 3

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• Dotty 0.21.0-RC1: feature complete for Scala 3 (December 2019)
• 3.0.0 released on May 13, 2021
• Current release 3.3.0 released on May 30th, 2023
• IDE support
  • Visual Studio Code with Metals
    • integrated support in Metals including Scala Worksheet support!
  • IntelliJ
    • Scala 3 support with the Scala Plugin
• There's the Scala 3 Migration Guide!

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The Actor Model and Akka

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• As mentioned before, the Scala 2 application we'll be working with, uses the Akka toolkit and is composed of a number of so-called Actors
• Akka Actors are based on the Actor Model invented by Carl Hewitt in 1973
• The Actor Model provides:
  • A higher level of abstraction for writing concurrent and distributed applications
  • Alleviates the developer from having to deal with explicit locking and thread management
• An Actor is the base unit of computing in the Actor Model
• An Actor
  • Has an address (of type ActorRef)
  • Can send messages to other Actors
  • Can create other Actors
  • Has a behaviour that can potentially change after processing a message

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Akka Actors - Protocol Definition

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• An Actor has a Protocol that defines
  • The message [types] it can process: so-called Commands
  • The messages it can send in response: so-called Responses