multiple inheritance problem when interfacing C++ object in perlXS

[Franck . Caron]

Hi,

I have some object with multiple inheritance : 

class D : public B1, public B2

B1   B2
  \    /
    D

I made XS interface for B1,B2 and D classes, 
and I set ISA to match inheritance in the perl packages

 I have a function that have parameters from type B2 
and I want to pass a D to this function.

int func(B2* obj1,B2* obj2){
        return  obj1 == obj2;
}

D* d_ptr = new D();
B2* b2_ptr = dynamic_cast<B2*>(d_ptr)
func(d_ptr,b2_ptr);

>> return true


this works fine in full C++
but in the XS mapping the following process is in action:

D* object is cast on a void* to be came a perl reference.
then this void * is cast into a B2*.

here is my perlobject.map:

# "perlobject.map"  Dean Roehrich, version 19960302
#
# TYPEMAPs
#
######################################################################
OUTPUT
 
# The Perl object is blessed into 'CLASS', which should be a
# char* having the name of the package for the blessing.
T_X_PTR
        sv_setref_pv( $arg,${ntype}_Package, (void*)$var );
 
######################################################################
INPUT
 
T_X_PTR
        if(sv_derived_from($arg,${ntype}_Package)) { 
                IV tmp_ = SvIV((SV*)SvRV($arg));
                $var = ($type)tmp_;
        }
        else    
                croak(\"$var is not of type %s\",${ntype}_Package);
 


if I compare the final B2* and the original D*, the address of the pointed object
has changed due to the void* cast that do not work correctly with multiple inheritance.

This is a problem for me because I compare addresses of objects. so that the function
return false!!

Do you know how to fix this?
Is there a safe way to map multiple inherited objects in perl ??


thanks 


Franck