[boost] Re: Re: dynamic_void_cast

From: Eric Woodruff (Eric.Woodruff_at_[hidden])
Date: 2002-12-11 10:16:23

"Johan Nilsson" <johan.nilsson_at_[hidden]> wrote in message
news:at76e1$2ro$1_at_main.gmane.org...
>
> "Eric Woodruff" <Eric.Woodruff_at_[hidden]> wrote in message
> news:at542o$2hq$1_at_main.gmane.org...
> >
> > "Johan Nilsson" <johan.nilsson_at_[hidden]> wrote in message
> > news:at52vi$si6$1_at_main.gmane.org...
> > [snip]
> >
> > > I'd like to be able to store references to objects of arbitrary types
in
> a
> > > homogenous collection, not requiring them to be derived from a common
> base
> > > class. For COM users, that would be something like an "IUnknown in the
> > > context of standard C++". I suspect that boost::any might be something
> > > similar to what I need, but I just got that idea using void pointers.
> > >
> >
> > What's the point of that? I mean, with no interface to the types, you
> can't
> > do anything with these objects you're storing, not even delete them.
> >
>
> If I can dynamically cast a void pointer to a polymorphic type, I can do
> whatever I want to do.
>
> > You could also do:
> >
> > struct IHolder {
> >     virtual ~IHolder () {}
> > };
> >
> > template <typename Object>
> > class holder : public IHolder{
> >     public:
> >         holder (Object* const object);
> >         ~holder ();
> > };
> >
> > It's always better to try and look for a real (type safe) solution than
> > playing around with type casting. It still depends on what you want to
> _do_
> > with theses objects behind this common, empty interface. I suspect
> problems
> > with your design if you have been led down this path.
> >
>
> I _am_ looking for a type safe solution, I was simply playing around
trying
> to find one that would fit my needs.
>
> I'm actually experimenting with a kind of 'generic' object factory with
the
> following characteristics:
>

Well then void* is not what you need. Especially in your design, you may
later decide that need to not only delete these objects in the factory, but
do other things with them as well.

I think you need to reanalyze what your needs are and the important roles in
this system. It seems to be that there is more than one class necessary
here.

Anyhow, in my opinion, dynamic_void_cast is completely unnecessary and takes
casts away the intent that it is _supposed_ to be a two step and very ugly
process--the signifier that you have a not-so-good design on your hands.
Stop trying to code a new messenger.

[snip]