An example to send messages among actors on different actor systems

master.cpp

#include "caf/all.hpp"
#include "caf/io/middleman.hpp"

using namespace caf;

class Master : public caf::event_based_actor {
public:
  caf::actor inner;

  Master(caf::actor_config &cfg, caf::actor inner) : event_based_actor(cfg) {
    this->inner = inner;
    this->send(inner, std::string("hello"));
  }

  caf::behavior make_behavior() override {
    return {
      [=](std::string world) {
        std::cout << "receive world" << std::endl;
      },
      [&](caf::actor other_inner) {
        this->send(this->inner, other_inner);
        std::cout << to_string(other_inner.address()) << std::endl;
      }
    };
  }
};

class Inner : public caf::event_based_actor {
public:
  Inner(caf::actor_config &cfg) : event_based_actor(cfg) {}

  caf::behavior make_behavior() override {
    return {
      [=](std::string hello) {
        return std::string("world");
      },
      [=](caf::actor other) {
        std::cout << "sending secret" << std::endl;
        this->send(other, 31415926);
      }
    };
  }
};

int main(int argc, char **argv) {
  caf::actor_system_config cfg;
  cfg.load<caf::io::middleman>();
  caf::actor_system sys{cfg};
  caf::actor_system sys2{cfg};

  caf::actor inner = sys2.spawn<Inner>();
  caf::actor master = sys.spawn<Master>(inner);
  sys.middleman().publish(master, 12341);
}

worker.cpp

#include "caf/all.hpp"
#include "caf/io/middleman.hpp"

using namespace caf;

class Worker : public caf::event_based_actor {
public:
  caf::actor master, inner;

  Worker(caf::actor_config &cfg, caf::actor master, caf::actor inner) : event_based_actor(cfg) {
    this->master = master;
    this->inner = inner;
    this->send(inner, std::string("Hello"));
  }

  caf::behavior make_behavior() override {
    return {
      [=](std::string world) {
        std::cout << caf::to_string(inner.address()) << std::endl;
        this->send(master, inner);
      }
    };
  }
};

class Inner : public caf::event_based_actor {
public:
  Inner(caf::actor_config &cfg) : event_based_actor(cfg) {}

  caf::behavior make_behavior() override {
    return {
      [=](std::string hello) {
        return std::string("world");
      },
      [=](int secret) {
        std::cout << secret << std::endl;
      }
    };
  }
};

int main(int argc, char **argv) {
  caf::actor_system_config cfg;
  cfg.load<caf::io::middleman>();
  caf::actor_system sys{cfg};
  caf::actor_system sys2{cfg};

  caf::actor inner = sys2.spawn<Inner>();
  caf::actor master = sys.middleman().remote_actor<caf::actor>("127.0.0.1", 12341).value();
  caf::actor worker = sys.spawn<Worker>(master, inner);
}