template <class T>
class raw_assignment_shim
{
public:
   operator T::resource_type*() // conversion op
   {  return &res_; }

   ~raw_assignment_shim()       // dtor
   {
      // do some checks here...
      ref_.set(res_, false);
   }

private:
  
   friend raw_assignment_shim<T> make_raw_assignment_shim(T& ref);

   raw_assignment_shim(T& ref): // private ctor
      res_(ref.get()),
      ref_(ref)
   {}

   T::resource_type operator*(); // not implemented. Prevents de-ref.

private:

   T::resource_type res_;
   T& ref_;
};


template <class T>
raw_assignment_shim<T> make_raw_assignment_shim(T& ref)
{  return raw_assignment_shim<T>(ref); }


///////////////////////////////////////////////////////////////////////////////////

bool SequenceProcessor::createFilterGraph(string filename)
{
   using winstl::a2w;

   // Create a source filter specified by filename
   ref_ptr<IBaseFilter> pSource;
   if(FAILED(pGraph->AddSourceFilter(a2w(filename),0, make_raw_assignment_shim(pSource))))
   {
      ::MessageBox( NULL, "Unable to create source filter",
                   "Error", MB_OK | MB_ICONINFORMATION );
      return 0;
   }

/* // original code...
   // Create a source filter specified by filename
   ref_ptr<IBaseFilter> pSource;
   {
      IBaseFilter* ppSource= NULL;

      if(FAILED(pGraph->AddSourceFilter(a2w(filename),0,&ppSource)))
      {
         ::MessageBox( NULL, "Unable to create source filter",
                      "Error", MB_OK | MB_ICONINFORMATION );
         return 0;
      }
      pSource.set(ppSource, false);
   }
*/
   ...