Re: boost weak pointers and boost optional

From:

Peter Dimov <pdimov@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 17 Jul 2008 12:06:41 CST

Message-ID:

<fefd3df6-24e5-4df0-96a4-72a4e992fd8a@i76g2000hsf.googlegroups.com>

On Jul 17, 11:21 am, Thant Tessman <thant.tess...@gmail.com> wrote:

In the case of weak pointers, it would have to look more like:

        struct nothing {};

        template <typename T>
        struct weak_pointer {

            /* ...*

            typename boost::variant<nothing,shared_ptr<T> > Optional;

            Optional lock() const;

            /* ... */
        }

Right. So how does user code look like?

1.

Optional opt = wp.lock();

if( shared_ptr<T>* p = boost::get< shared_ptr<T> >( &opt ) )
{
  // use **p
}
else
{
  // do not use p
}

2.

Optional opt = wp.lock();

try
{
  shared_ptr<T> const& r = boost::get< shared_ptr<T> >( opt );
  // use *r
}
catch( boost::bad_get )
{
  // ...
}

3.

struct visitor
{
  typedef void result_type;
  void operator()( shared_ptr<T> const & p ) const { ... }
  void operator()( nothing ) const { ... }
};

boost::apply_visitor( visitor(), wp.lock() );

Which one of these is an improvement?

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