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

From: Douglas Gregor (gregod_at_[hidden])
Date: 2001-07-24 11:46:58

On Tuesday 24 July 2001 09:04, you wrote:
> From: <greg_at_[hidden]>
>
> > This looks like a good start, thanks.  I think do_dynamic_cast is the
> > name we previously agreed on for your shared_dynamic_cast, and that
> > we wanted a version that worked for raw pointers as well.
>
> If do_dynamic_cast is supposed to be a generalization of dynamic_cast:
>
> template<class R, class T> R do_dynamic_cast(T /* const */ &);
>
> (dynamic_cast<U*> returns U*, dynamic_cast<U&> returns U&)
>
> then dynamic-casting a shared_ptr would look like
>
> do_dynamic_cast<shared_ptr<X> >(y); // 1
>
> whereas with a shared_ptr-specific cast the syntax would be
>
> shared_dynamic_cast<X>(y); // 2
>
> I prefer (2). (1) is more generic but I can't see how the genericity would
> be exploited.
>
> --
> Peter Dimov
> Multi Media Ltd.

(1) also has the advantage of being syntactically identical to dynamic_cast. 
It seems like a named cast that doesn't cast exactly to the type named in the 
angle brackets shouldn't have the postfix _cast.

To make do_dynamic_cast<> really useful for functions accepting generic 
pointer-like types, one might also need the ability to rebind a pointer, i.e.,

        pointer_rebind<boost::shared_ptr<int>, float>::pointer

would return the type boost::shared_ptr<float>. Then it would be possible to 
write code to accept generic pointer types and perform casts on them with 
do_dynamic_cast<>.
 
        Doug