Re: [boost] Re: downcasting smart pointers (suggested code)

From: Peter Dimov (pdimov_at_[hidden])
Date: 2001-07-24 15:24:02

From: "Greg Colvin" <gcolvin_at_[hidden]>
[...]

>     template<typename BasePtr, typename DerivedPtr>
>     DerivedPtr whatever(BasePtr in) {
>        ...
>        DerivedPtr p = do_dynamic_cast<DerivedPtr>(in);
>        ...
>        return p;
>     }

Or something like

template<class Ptr> void whatever(Ptr p)
{
   if(IDrawable q = do_dynamic_cast<IDrawable>(p)) q->draw();
}

where IDrawable is typedef'ed somewhere to be, say, shared_ptr<Drawable>.

(As an aside, people like to implement their own COM-like component systems;
it would be great if shared_ptr<> can be used for this. The two main
obstacles are (1) no 'queryInterface' support - this would hopefully be
addressed by do_dynamic_cast - and (2) a shared_ptr<> created in a DLL and
destroyed in the main program causes problems when different heaps are
used.)

Still, I prefer that shared_dynamic_cast<> be left as an option. More
focused (less generic) interfaces are less error prone, when genericity is
not required.

--
Peter Dimov
Multi Media Ltd.