[boost] Re: free_on_error

From: Jonathan Turkanis (technews_at_[hidden])
Date: 2005-05-01 16:06:22

Jason Hise wrote:
> Does a utility like the following already exist in boost?  If so, what
> is it called?  If not, is there interest in adding it?
>
>     template < typename Function >
>     struct free_on_error
>     {
>     private:
>         Function function_;
>         bool reset_;
>
>     public:
>         free_on_error ( Function function ) :
>             function_ ( function ),
>             reset_    ( true )
>         {
>         }
>
>         ~ free_on_error (  )
>         {
>             if ( reset_ )
>             {
>                 function_ (  );
>             }
>         }
>
>         void discard (  )
>         {
>             reset_ = false;
>         }
>     };
>
> This would be used to make certain operations exception safe.  For
> example:
>
> A * foo (  )
> {
>     A * a = new A (  );
>     free_on_error < BOOST_TYPEOF ( lambda::bind ( delete _1, a ) ) >
>         release ( lambda::bind ( delete _1, a ) );
>     a->DoSomethingThatMightThrow (  );
>     release.discard (  );
>     return a;
> }

It sounds like you may be looking for Petru and Andrei's ScopeGuard:
http://tinyurl.com/26vzp. (BTW, has anyone noticed http://www.scopeguard.com/ ?)

It uses a neat trick to avoid specifying the return type of bind or  lambda
expressions. A version of ScopeGuard exists as an implementation detail of
multi_index. Previously, I had used a ScopeGuard in iostreams, and was planning
to move it to boost/detail. Unfortunately it caused problems with borland 5.x,
Metrowerks 8.3 and VC6, so I excised it.

Jonathan