Re: [boost] [smart_ptr] Some questions

From: Daniel Frey (d.frey_at_[hidden])
Date: 2008-04-10 09:57:40

On Thu, 2008-04-10 at 09:27 -0400, Frank Mori Hess wrote:
> On Thursday 10 April 2008 06:40 am, Daniel Frey wrote:
> > On Wed, 2008-04-09 at 20:13 -0400, Frank Mori Hess wrote:
> > I attached a minimalistic patch against the trunk which enhances the
> > current code into that direction.
> 
> The static_cast in your patch is going to have problems with virtual base 
> classes.  I think you could just use the Y* available in 
> sp_enable_shared_from_this and call _internal_accept_owner from that.

Note that 5.2.9/8 only refers to B and D's relationship. Since we are
creating a new base class, we can define that non-virtual derivation is
a precondition. In the patch I've shown the static_cast should be
perfectly legal and it should work in all cases, AFAICT.

> Also, on further thought, I don't think enable_shared_from_this_base needs to 
> be a template class at all.

If you have an easier implementation without further overhead, I'd be
happy to see it.

> > The name (enable_shared_from_this_base) is probably not a good name. I
> > think that from shared_ptr's point of view, it doesn't need to know what
> > the callback is used for. It might be better to call it
> > notify_on_ownership or something in that direction. And the callback
> > function should probably also be renamed. Suggestions?
> 
> I agree.  notify_on_ownership seems ok.  Some other possibilities are 
> ownership_observer or shared_ptr_observer.  The callback might be 
> accept_shared_ptr_owner() or update_shared_ptr_owner()

Those are excellent suggestions. I think shared_ptr_observer and
update_shared_ptr_owner are the names I like most.

> Also, I don't think enable_shared_from_this should actually use this base 
> class in the end, whatever it is called (although it is a good test).  If it 
> does, the user will have to take special care to avoid problems when deriving 
> from both enable_shared_from_this and this base class.  This might happen if 
> the user is deriving from the base class for purposes other than 
> re-implementing enable_shared_from_this.

Good point. I'll need some time to think about this case.

Regards, Daniel