basic actor model in golang https://go.dev/play/p/D3RQkzRHcJX

actors.go

package main

import "log"

type CounterMessage int

func main() {
	var a1 *Actor
	var a2 *Actor

	// Actor 1 pings actor 2 and shuts itself down when count reaches 0.
	a1 = NewActor(func(message any) {
		log.Printf("actor1: %v", message)
		switch v := message.(type) {
		case CounterMessage:
			if v == 0 {
				a1.Stop()
				return
			}
		}
		// Respond to actor2.
		a2.inbox <- "ping"
	})

	// Stateful a2 actor.
	n := CounterMessage(32)
	a2 = NewActor(func(message any) {
		log.Printf("actor2: %v", message)
		n -= 1
		a1.inbox <- n
	})
	defer a2.Stop()
	go a2.Start() // Kick off a2

	// Kick off first message
	a2.inbox <- "hello"

	// Program waits for a1 to finish.
	a1.Start()
}

func NewActor(handleFunc func(any)) *Actor {
	return &Actor{
		handleFunc: handleFunc,
		inbox:      make(chan any),
		done:       make(chan struct{}),
	}
}

type Actor struct {
	handleFunc func(any)
	inbox      chan any
	done       chan struct{}
}

func (a *Actor) Start() {
	for {
		select {
		case <-a.done:
			return
		case message := <-a.inbox:
			a.handleFunc(message)
		}
	}
}

func (a *Actor) Stop() { close(a.done) }