There are some cases where _narrow() needs to make remote invocations.
Because this is expensive you can tell the IDL whether or not to
generate code that makes remote invocations using --query-server-for-narrow.
The following discussion explains when you have to use
--query-server-for-narrow.


Consider the following scenario: you have a server which maintains
references to an interface called "base". This server is defined by
the files base.idl, base_impl.[h|cc] and server.cc. Once the server is
compiled and linked, it is started.

At a later point in time someone decides to define a new interface
"derived" which inherits from "base". The client makes use of both
base and derived and therefore needs all the files in this directory.

What happens if the server, which is still running, is getting a
reference to "derived"? It should pose no problems according to the
CORBA subtyping rules. But how does the server know that "derived"
IS-A "base".

One way would be to stop the server, re-link it with the
implementation of derived and then get it up and running again.
Sometimes it is not desirable to stop the server. In that case the
only way for the server to know about "derived" IS-A "base" is to
ask the client that generated the "derived" object.

Since this means a significant time overhead (each failed _narrow()
will do a query to the server), we have added a new command line option
for the IDL compiler. The code generated for _narrow() only queries
the server if you use the --query-server-for-narrow switch.

Beware of the extra IDL compiler switch in the Makefile.

BTW: the content of this README should be moved to the docs...