From: Jeff Sack <jeff.sack@...>
Date: 2007-01-12T07:20:06+09:00
Subject: SWIG, Ruby, C and typemaps


Hello all.  I am seeking some advice on using SWIG to wrap some native
C code provided to me (I don't have the ability to change it).
Basically, I have something like this:

The definition of one of the problematic methods I am trying to wrap
looks something like this.  This is in my SWIG interface file (.i
file):

int open_file(ResponseObject **resp, const char *fname);

And the normal way of using this is as follows:

ResponseObject *reponsObj;
const char *filename="input_file";

if(open_file(&reponsObj, filename)!=0)
{
  // handle non-zero error code
}
else
{
  // success!
}


I think the most natural way of accessing this method might be
something like this:

resp = open_file('input_file')

In this scenario, resp is a Ruby object representing ResponseObject,
and the original int return value is now mapped to a conditionally
thrown exception.  If open_file returns 0, then no exception would be
thrown, otherwise, the Ruby method open_file would throw an exception
which wraps the int return code.

Thoughts?  I know there is some SWIG/typemap magic that can do this,
but so far I'm a bit stumped.  Can someone offer some advice?  I can
provide more details if needed.

Thanks so much in advance for your help.  Much appreciated.

-Jeff