so-5.5.1: Subscribing an agent events via state_t::event method

The traditional way for subscribing an agent events is so_subscribe().in().event() chain. But sometimes this way is too verbose. Because of that since v.5.5.1 it is possible to subscribe an agent's event via new so_5::rt::state_t::event() methods. For example those two so_define_agent() methods do exactly the same things.

A traditional approach:

void my_agent::so_define_agent()
{
  so_subscribe_self().in( st_not_connected )
    .event( &my_agent::evt_connected )
    .event( &my_agent::evt_connect_failed );
 
  so_subscribe_self().in( st_connected )
    .event( &my_agent::evt_close_connection )
    .event( &my_agent::evt_incoming_data )
    .event( &my_agent::evt_disconnected );
 
  so_subscribe( m_configurator_mbox ).in( st_not_connected )
    .event( &my_agent::evt_change_config_when_disconnected );
  so_subscribe( m_configurator_mbox ).in( st_connected )
    .event( &my_agent::evt_change_config_when_connected );
}

A new approach:

void my_agent::so_define_agent()
{
  st_not_connected
    .event( &my_agent::evt_connected )
    .event( &my_agent::evt_connect_failed );
 
  st_connected
    .event( &my_agent::evt_close_connection )
    .event( &my_agent::evt_incoming_data )
    .event( &my_agent::evt_disconnected );
 
  st_not_connected
    .event( m_configurator_mbox,
            &my_agent::evt_change_config_when_disconnected );
  st_connected
    .event( m_configurator_mbox,
            &my_agent::evt_change_config_when_connected );
}

The main difference in those methods is inability to subscribe the one event for several states by state_t::event() method chain. A traditional approach must be used in such case:

void my_agent::so_define_agent()
{
  so_subscribe_self()
    .in( st_not_connected )
    .in( st_waiting_auth_result )
    .in( st_waiting_reconnect )
    .in( st_reconfig_failed )
    .event( &my_agent::evt_get_status_when_no_connection );
 
  st_connected.event( &my_agent::evt_get_status_when_connected );
}