Re: [Boost-users] <smart_ptr> scoped_ptr with a Deleter

From: me22 (me22.ca_at_[hidden])
Date: 2006-02-03 09:40:17

On 03/02/06, Loïc Joly <loic.joly_at_[hidden]> wrote:
> Guy Peleg a écrit :
> > Hi,
> >
> > How come scoped_ptr can't work with a special
> > 'deleter' as shared_ptr?
>
> I was just wondering the same thing. This would be quite convenient for
> me, where I just want to use RAII without redefining the ressource
> holding class. I agree that I could just use shared_ptr anyway for this
> purpose, but scoped_ptr would be documenting my intent more precisely.
>

It's my understanding that scoped_ptr does not allow the custom
deleter since shared_ptr does it by keeping a boost::function<> ( or
perhaps some other similar utility ) to the deleter, which, if used
for scoped_ptr, would make a scoped_ptr larger than a plain pointer (
by about 2 pointers ) and would make the destructor slower ( by about
1 call through a function pointer ), which would be unacceptable for
many users of scoped_ptr.  In any case, the speed difference between a
shared_ptr and some scope pointer that did keep a boost::function<> to
a deleter would only be in the allocation of the reference count
which, especially with the quick allocator, is usually not that
severe.

One possibility, however, would be for a deleter_scoped_ptr ( that's
not yet written ) to have a second template argument of a functor that
would be default-constructed and then called on the pointer as the
deleter.  That would eliminate the speed and size overhead, but it
means much less flexibility in what the deleter can be ( since it must
be set at declaration, which means no binders or function pointers,
among other things ).

~ Scott McMurray