[boost] Re: boost::shared_ptr<> and the pimpl idiom

From: Dave Abrahams (abrahams_at_[hidden])
Date: 2000-01-17 13:51:04

> Unfortunately, this does not work smoothly: I need to define the
> class to be used as template argument to the 'boost::shared_ptr' in the
> header to make it work. One option would be something like this:
>
>   // directory.hpp:
>   struct representation { virtual ~representation(); };
>   class dir_it {
>     // ...
>   private:
>     boost::shared_ptr<representation> m_rep;
>   };
>
> ... and use a class derived from 'representation' in the implementation.
> However, this is rather inconvenient since I would have to cast the
> pointer whenever I want to access it, ie.
>
>   static_cast<real_representation*>(m_rep)->m_member ...
>
> Now, what are the options to avoid this? I don't think that there is any
> using the type 'boost::shared_ptr'

There is no reason you should need to do this provided you have an
out-of-line definition for the destructor of dir_it. You should be able to
simply provide a forward declaration of the representation class. I do that
all the time

   class dir_it {
     ~dir_it();
   private:
     class representation;
     boost::shared_ptr<representation> m_rep;
   };

-Dave

P.S. I'd much prefer abbreviation of "representation" to abbreviation of
"directory_iterator" ;)