An example code for https://blog.oklahome.net/2018/09/protoactor-go-messaging-protocol.html

no-sender-to-respond.go

package main

import (
	"github.com/AsynkronIT/protoactor-go/actor"
	"log"
	"time"
)

type pong struct {
}

type ping struct {
}

type pingActor struct {
	pongPid *actor.PID
}

func (p *pingActor) Receive(ctx actor.Context) {
	switch ctx.Message().(type) {
	case struct{}:
		// Below does not set ctx.Self() as sender,
		// and hence the recipient has no knowledge of the sender
		// even though the message is sent from another actor via actor.Context.
		//
		ctx.Tell(p.pongPid, &ping{})

	case *pong:
		log.Print("Received pong message")

	}
}

func main() {
	pongProps := actor.FromFunc(func(ctx actor.Context) {
		switch ctx.Message().(type) {
		case *ping:
			log.Print("Received ping message")

			// 2018/09/15 02:01:27 [ACTOR] [DeadLetter] pid="nil" message=&{} sender="nil"
			ctx.Respond(&pong{})

			// 2018/09/15 02:01:27 [MAILBOX] [ACTOR] Recovering actor="nonhost/$1" reason="runtime error: invalid memory address or nil pointer dereference" stacktrace="github.com/AsynkronIT/protoactor-go/actor.(*PID).ref:26"
			// 2018/09/15 02:01:27 [ACTOR] [SUPERVISION] actor="nonhost/$1" directive="RestartDirective" reason="runtime error: invalid memory address or nil pointer dereference"
			ctx.Sender().Tell(&pong{})

		default:

		}
	})
	pongPid := actor.Spawn(pongProps)

	pingProps := actor.FromProducer(func() actor.Actor {
		return &pingActor{
			pongPid: pongPid,
		}
	})
	pingPid := actor.Spawn(pingProps)
	pingPid.Tell(struct{}{})
	time.Sleep(1 * time.Second) // Just to make sure system ends after actor execution
}