# The main message type.
# Must begins by the header.
# Following a basic scheme, it could be a switch case depending on
#  the MSG_ID_FIELD_NAME field which is inside MSG_HEADER_TYPE.
MSG_MAIN_TYPE      T_msg_switch(Type)



It is not mandatory to specify the MSG_MAIN_TYPE like this.



E.g. add into your .fdesc file :
struct  T_msg_main_type
{
  T_msg_switch(Type)    "";
}

Then, into your .wsgd file, the following line is strictly equivalent to the 1st declaration :
MSG_MAIN_TYPE      T_msg_main_type



So you can do, for example :
struct  T_msg_main_type
{
  T_msg_header_type     header;
  T_data_switch(Type)   "";        # switch for the data part (after header), not for the entire msg (including header)
}



If your message only contains an header :
struct  T_msg_main_type
{
  T_msg_header_type     "";
}
Or more directly :
MSG_MAIN_TYPE      T_msg_header_type



And whatever ...