Hi,

  I wrote a little proof-of-concept shim for doing this.
It seems to work as expected, while preventing naive misuse.

    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);
       }
    */
       ...

Of course, the names can be changed, and some refinements should
probably be added.
Such as limit it only for initializing an empty (NULL) ref_ptr<>,
exceptions etc.

What do you think?
Adi

Any comments on this?

Adi Shavit wrote:
> Hi,
>
>   I wrote a little proof-of-concept shim for doing this.
> It seems to work as expected, while preventing naive misuse.
>
>     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);
>        }
>     */
>        ...
>
> Of course, the names can be changed, and some refinements should
> probably be added.
> Such as limit it only for initializing an empty (NULL) ref_ptr<>,
> exceptions etc.
>
> What do you think?
> Adi
>
>
>

There will be.

Am crammed with the very last bits of XSTL - CD, index, final page proofs.

After that, things will be more 'Active'. (Get it?!?! <g>)
  "Adi Shavit" <adish@gentech.co.il> wrote in message news:f0vcml$kcd$1@digitalmars.com...
  Any comments on this?

  Adi Shavit wrote:
    Hi,

      I wrote a little proof-of-concept shim for doing this.
    It seems to work as expected, while preventing naive misuse.

      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);
         }
      */
         ...

    Of course, the names can be changed, and some refinements should probably be added.
    Such as limit it only for initializing an empty (NULL) ref_ptr<>, exceptions etc.

    What do you think?
    Adi