Re: [boost] [smart_ptr] Some questions

From: Daniel Frey (d.frey_at_[hidden])
Date: 2008-04-10 06:40:11

On Wed, 2008-04-09 at 20:13 -0400, Frank Mori Hess wrote:
> On Wednesday 09 April 2008 17:26 pm, Daniel Frey wrote:
> > On Wed, 2008-04-09 at 17:06 -0400, Frank Mori Hess wrote:
> > > think of.  Of course, you would still be inflicted with a vtable, but
> > > that doesn't add any per-object space overhead, which seems to be what
> > > you're most concerned about.
> >
> > A vtable means that the per-object size *does* grow, since each object
> > needs a pointer to the vtable.
> 
> Oh, yeah.  Well, it could be done generically too without even a vtable, if 
> shared_ptr recognized a template class which the user could define 
> specializations of.

I attached a minimalistic patch against the trunk which enhances the
current code into that direction.

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?

The next logical step would be to add another ctor for the
low_overhead_enable_shared_from_this, i.e. a ctor for shared_ptr which
takes a plain pointer and a weak_count or a shared_count?). Or it might
be possible to generalize that case with the current special ctor that
takes the ignore_enable_shared_from_this_tag, but that's a second patch
on top of the first one, which I will try to write when my time permits.

Regards, Daniel