[geos-devel] Design of exception-trapping wrapper

David Blasby dblasby at refractions.net
Fri Apr 11 20:33:20 EDT 2003

Martin Davis wrote:

>Does anyone have time and ideas to prototype the design of this wrapper?  I'm not sure I understand the problem quite well enough yet to propose a design.   A small mockup might help to clarify the situation.
Something like the function included below.
NOTE: this is an *added* interface, not the ONLY interface.  C++ and 
simple C programs could use the system exactly the way it is now.

We'd have to come up with name so we dont have any redundant symbols.

 >>This seems like a pretty substantial change to GEOS.

No - I think it would be pretty easy.  We could add another class to 
GEOS.  It wouldnt even have to be compiled unless you're using postgis...

Unfortunately, there could be a lot of these little functions.  But, if 
we stick to just wrapping the Geometry interface, we should be okay.  I 
dont think postgis requires more than this.

// call g1->contains(g2)
// returns 0 = false
//         1 = true
//         2 = error was trapped
char GEOSrelateContains(Geometry *g1, Geometry*g2)
   try {
       bool result;
       result = g1->contains(g2);
       if (result)
           return 1;
           return 0;
   catch (...)
       return 2;

The postgis_wrapper.cpp would be very simple:

char relate(Geometry *g1, Geometry *g2)
     return  GEOSrelateContains(g1,g2);

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