[boost] Re: dynamic_cast for shared_ptr

From: Kevlin Henney (Kevlin.Henney_at_[hidden])
Date: 2000-02-08 11:09:31

Miki Jovanovic wrote:
>Here is my proposition for dynamic_cast for shared_ptr. Would this be
>of value?
[snip]

This seems quite involved compared with the one posted on this list a few
weeks ago:

      template<typename Target, typename Source>
      inline shared_ptr<Target> dynamic_shared_cast(const
shared_ptr<Source> & arg)
      {
          shared_ptr<Target> result;

          if(Target * got = dynamic_cast<Target *>(arg.px))
          {
              result.px = got;
              delete result.pn;
              ++*(result.pn = arg.pn);
          }

          return result;
      }

The only inefficiency here is that an unused count is allocated and then
discarded because shared_ptr currently counts nulls. My own counted pointer
implementations do not and the control flow was lifted pretty much
straight.

Kevlin