[Swig-user] extend_smart_pointer and vectors

[Luke M. <lu...@si...>]

Luke Moore wrote:
 > Thank you very much.  It works beautifully.
 >
 > -Luke
 >
 > Marcelo Matus wrote:
 >> Check the refcount.i example and the %extend_smart_pointer macrlo. I
 >> think that solves
 >> most of the issues with smart pointers  and smart pointers + vectors.
 >>
 >> Marcelo

%extend_smart_pointer has worked great, but I've since run into a case 
that doesn't work.

Here's a simple example describing the problem.  Swig is wrapping a 
class named C, and I'm using boost::shared_ptr as the smart pointer.  I 
have a function that takes a pointer to a C object named foo():
     void foo(C* c);
a function that returns a single shared pointer, createSingle():
     boost::shared_ptr<C> createSingle();
and a function that returns multiple shared pointers, createMulti():
     std::vector<boost::shared_ptr<C> > createMulti()

foo(createSingle()) works without a problem.  foo(createMulti()[0]) 
raises a TypeError because it can't convert to a C*.  It seems to be 
because the C* isn't added to the swig object's "this" list:

 >>> foo.createSingle().this
<Swig Object of type 'boost::shared_ptr<C > *' at 0x81a4540><Swig Object 
of type 'C *' at 0x8152438>
 >>> foo.createMulti()[0].this
<Swig Object of type 'boost::shared_ptr<C > *' at 0x8146a08>

Looking at the wrapper code, createSingle() is applying the SMARTPOINTER 
typemap from pytypemaps.swg, calling __deref__ and adding the result to 
"this".  createMulti() is calling swig::from() on shared pointer, which 
I think eventually calls swig::traits_from_ptr<...>::from(), calling 
SWIG_NewPointerObj() but not applying the typemap.

If I manually specialize traits_from_ptr for my shared pointer, I 
believe it works:

%{
namespace swig {
   template <> struct traits_from_ptr<boost::shared_ptr<C> > {
     static PyObject *from(boost::shared_ptr<C> *val, int owner = 0) {
       PyObject *resultobj = SWIG_NewPointerObj(val, 

                          type_info<boost::shared_ptr<C> >(), owner);
       if (resultobj) {
          PyObject *robj = PyObject_CallMethod(resultobj,
                                         "__deref__", NULL);
          if (robj && !PyErr_Occurred()) {
            PySwigObject_append((PyObject *)
                                 SWIG_Python_GetSwigThis(resultobj),
           (PyObject *)SWIG_Python_GetSwigThis(robj));
           Py_DECREF(robj);
         }
       }
       return resultobj;
     }
   };
}
%}

Shouldn't the typemap do this specialization automatically, though?

Note that I'm using
     %extend_smart_pointer(boost::shared_ptr<C>);
     %template(_CShrdPtr) boost::shared_ptr<C>;
     %template(_CShrdPtrList) std::vector<boost::shared_ptr<C> >;
and I'm running swig 1.3.29.

Thanks for any help.

-Luke