return {

[=](pong_atom, int value) -> message {

if (!self->current_sender()) {

CAF_PRINT("last_sender() invalid!");

}

CAF_PRINT("received {'pong', " << value << "}");

// cout << to_string(self->current_message()) << endl;

if (++s_pongs >= num_pings) {

CAF_PRINT("reached maximum, send {'EXIT', user_defined} "

<< "to last sender and quit with normal reason");

self->send_exit(self->current_sender(),

exit_reason::user_shutdown);

self->quit();

}

return make_message(ping_atom::value, value);

},

others >> [=] {

CAF_PRINTERR("unexpected; " << to_string(self->current_message()));

self->quit(exit_reason::user_shutdown);

}

};

return {

[](ping_atom, int value) -> message {

CAF_PRINT("received {'ping', " << value << "}");

return make_message(pong_atom::value, value + 1);

},

others >> [=] {

CAF_PRINTERR("unexpected; " << to_string(self->current_sender()));

self->quit(exit_reason::user_shutdown);

}

};