Is it possible to use inheritance with typed actors in the C++ Actor Framework?

Question

The C++ Actor Framework allows actors to be strongly typed. Does the framework also support inheritance with typed actors?

Answer 1

Yes - a typed_actor instance can be treated as a different typed_actor type as long as the new type responds to a subset of the messages the instance supports. Here's an example where c_type/C is a super type of both a_type and b_type:

#include <iostream>
#include "caf/all.hpp"

using namespace caf;
using namespace std;

using a_type = typed_actor<replies_to<int>::with<void>>;
using b_type = typed_actor<replies_to<double>::with<void>>;
using c_type = a_type::extend<replies_to<double>::with<void>>;

class C : public c_type::base
{
protected:
    behavior_type make_behavior() override
    {
        return
        {
            [this](int value)
            {
                aout(this) << "Received integer value: " << value << endl;
            },
            [this](double value)
            {
                aout(this) << "Received double value: " << value << endl;
            },
            after(chrono::seconds(5)) >> [this]
            {
                aout(this) << "Exiting after 5s" << endl;
                this->quit();
            }
        };
    }
};

void testerA(const a_type &spawnedActor)
{
    scoped_actor self;
    self->send(spawnedActor, 5);
}

void testerB(const b_type &spawnedActor)
{
    scoped_actor self;
    self->send(spawnedActor, -5.01);
}

int main()
{
    auto spawnedActor = spawn<C>();
    testerA(spawnedActor);
    testerB(spawnedActor);
    await_all_actors_done();
}

Note: there is an example in the CAF 0.14.0 user manual showing how this works, but CAF 0.14.4 has removed the spawn_typed method that would make an inline creation/spawn of a typed_actor possible. See the corresponding GitHub issue for details.