hanishi

Zero-Cost Type Class Derivation for Scala 3 Opaque Types

Introduction

Scala 3's opaque type is one of the most compelling features for domain modeling. A single line gives you a brand-new type with zero runtime overhead.

opaque type UserId = String

hanishi

Inside the Pekko Actor Engine

A deep technical guide to how Apache Pekko actors work under the hood.

This document peels back the layers of the actor system -- starting from what you write as a user, then following your message all the way down to the thread pool, revealing the engineering decisions and trade-offs at each level. Every code snippet references the actual Pekko source.

Table of Contents

hanishi

import org.apache.pekko.actor.{Actor, Timers, Props}
  import scala.concurrent.duration.*

  object RetryActor {
    case object DoWork
    case class RetryWork(attempt: Int)
    case object WorkSucceeded
    case object WorkFailed

    private case object RetryTimerKey

hanishi

type CacheEntry<T> = {
    value: T,
    timeout: ReturnType<typeof setTimeout>,
}

class ExpiringCache<T> {
    private readonly cache: Record<string, CacheEntry<T>>;
    private readonly expirationTime: number;

    constructor(expirationTime: number = 5000) {

hanishi

package actors

import actors.CpcActuator.Actor.{ FetchMeasurementKey, TimeoutKey, Work }
import akka.actor.typed.scaladsl.{ ActorContext, Behaviors, StashBuffer, TimerScheduler }
import akka.actor.typed.{ ActorRef, Behavior, SupervisorStrategy }
import akka.util.Timeout
import com.google.inject.Provides
import play.api.Configuration
import play.api.libs.concurrent.ActorModule
import usecase.SamplePublisherService

hanishi

package actors

import akka.actor.typed.scaladsl.Behaviors
import akka.actor.typed.{ActorRef, Behavior}

import scala.collection.immutable
import scala.concurrent.duration.FiniteDuration
import scala.reflect.ClassTag
//see https://github.com/akka/akka/blob/v2.7.0/akka-actor-typed-tests/src/test/scala/docs/akka/typed/Aggregator.scala

hanishi

package example

import akka.Done
import akka.actor.typed.scaladsl.{
  ActorContext,
  Behaviors,
  StashBuffer,
  TimerScheduler
}
import akka.actor.typed.{ActorRef, Behavior, SupervisorStrategy}

hanishi

import typings.express.mod as express
import typings.express.mod.{RequestHandler, request_=}
import typings.expressServeStaticCore.mod.*
import typings.node.bufferMod.global.Buffer
import typings.node.processMod as process
import wvlet.airframe.log

import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.duration.DurationInt
import scala.concurrent.{ExecutionContext, Future}

hanishi

package example

import akka.actor.typed.ActorSystem
import akka.actor.typed.scaladsl.AskPattern.{Askable, schedulerFromActorSystem}
import akka.util.Timeout
import com.typesafe.config.ConfigFactory
import example.asyncHandler.{Req, Res}
import org.scalablytyped.runtime.StringDictionary
import typings.express.mod as express
import typings.node.bufferMod.global.Buffer

hanishi

package example

import akka.Done
import akka.actor.typed.scaladsl.{ActorContext, Behaviors, StashBuffer, TimerScheduler}
import akka.actor.typed.{ActorRef, Behavior, SupervisorStrategy}
import akka.pattern.StatusReply
import org.scalablytyped.runtime.StringDictionary
import typings.cheerio.cheerioMod.Cheerio
import typings.cheerio.mod.Node
import typings.devtoolsProtocol.mod.Protocol.Network.ResourceType