SObjectizer  5.7
so-5.5.9: New format of send function

Since v.5.5.9 the first argument to so_5::send() function can be either a reference to so_5::rt::mbox_t, a reference to so_5::rt::agent_t or a reference to ad-hoc definition proxy:

so_5::rt::mbox_t mbox = env.create_local_mbox();
auto engine = coop.make_agent<engine_agent>(...);
auto indicator = coop.define_agent();
...
// Old way of sending message via so_5::send():
so_5::send< get_status >(mbox);
so_5::send< get_status >(engine->so_direct_mbox());
so_5::send< get_status >(indicator.direct_mbox());
// New way:
so_5::send< get_status >(mbox);
so_5::send< get_status >(*engine);
so_5::send< get_status >(indicator);

It means that since v.5.5.9 so_5::send() can be used instead of so_5::send_to_agent().