Re: c++ faq 16.22 reference counting

From:

"Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 21 Jul 2010 11:42:49 +0200

Message-ID:

<i26fep$ol7$1@news.eternal-september.org>

* Vladimir Jovic, on 21.07.2010 11:35:

Reading 16.22 in c++ faq, I wondered why the assign operator wasn't
implemented like this :

FredPtr& operator= (FredPtr const& p)
{
    FredPtr tmp( p );

    std::swap( tmp, *this );

    return *this;
}

I haven't looked at the FAQ, but the call to std::swap here would invoke
FredPtr::operator=, recursively...

I think you meant something like

   FredPtr& operator=( FredPtr const& p )
   {
       FredPtr temp( p );
       swapWith( p );
       return *this;
   }

which can also be written as

   FredPtr& operator=( FredPtr const& p )
   {
       FredPtr( p ).swapWith( *this );
       return *this;
   }

or alternatively as the short & sweet

   FredPtr& operator=( FredPtr p )
   {
       swapWith( p );
       return *this;
   }

The effect should be the same. tmp goes out of scope, and old object is
destroyed (count is decreated, and old object deleted if count=0), and
new object is copy constructed, therefore the count is increased by 1.

Is this correct, or am I missing something?

Not sure. I'd guess the FAQ item is probably illustrating something else?

Cheers,

- Alf

--
blog at <url: http://alfps.wordpress.com>