Re: [boost] boost::shared_ptr/weak_ptr

From: Daniel Frey (d.frey_at_[hidden])
Date: 2008-04-12 12:17:51

On Sat, 2008-04-12 at 19:01 +0300, Peter Dimov wrote:
> Daniel Frey:
> > On Sat, 2008-04-12 at 17:31 +0300, Peter Dimov wrote:
> >> http://svn.boost.org/trac/boost/changeset/44344
> >
> > Wouldn't it be easier to make shared_count(weak_count&) to never throw
> > and add
> >
> > if(!pn) boost::throw_exception( boost::bad_weak_ptr() );
> >
> > to the non-tagged ctor of the shared_ptr?
> 
> No. Consider your proposed
> 
> +    template<class Y>
> +    explicit shared_ptr(detail::weak_count const & wc, Y * p): pn(wc) // 
> may throw
> +    {
> +        // it is now safe to copy p, as pn(wc) did not throw
> +        px = p;
> +    }
> 
> which would change meaning.

I'm currently happy with a single additional (and mostly internal) ctor,
namely

  template<class Y>
  shared_ptr(detail::shared_count & c, Y * p) ...

which can be used to solve all cases. Please see the updated patch. One
thing you can now do is, let enable_shared_from_this_light throw it's
own exception type (e.g. bad_shared_from_this) in case of misuse, as the
usage of a weak_ptr or weak_count is just an implementation detail.

It also allows to remove the whole sp_nothrow_tag stuff - no need for it
anymore...

Regards, Daniel