Re: [Boost-users] How to automatically release legacy resources?

From: Aaron W. LaFramboise (aaronrabiddog51_at_[hidden])
Date: 2005-01-22 03:04:21

Delfin Rojas wrote:

> I think this should work for all the cases you mention:
> 
> http://www.boost.org/libs/smart_ptr/sp_techniques.html#handle
> 
> http://www.boost.org/libs/smart_ptr/sp_techniques.html#on_block_exit

Thanks for this pointer!  In particular, I did not know about
smart_ptr's termination functor parameter.  This has very nice
semantics.  smart_ptr plus Boost.Lambda would be quite elegant:

shared_ptr<void> s(0, if_(bind(close, file_desc) == ..., ... ));

Well, sort of, anyway. :)  Its too bad that noone seems interested in
adding proper lambda expressions to C++.  bind() in particular is a pain.

Jonathan Turkanis makes an important point, though.  scope_guard uses
initializer lifetime rules to allow the abstract entity to live beyond
the end of the definition, without having to do any extra memory
allocation.  I don't beleive any smart_ptr- or boost::function-based
solutions will have this trait.  This could be an important performance
efficiency consideration when adopting an idiom to be used in general.

So, I suppose, real tests are in order, to see which of these approaches
really works on real compilers.  Of the four sorts of solutions
mentioned, only scopeguard and creating a throw-away class have any
chance of being optimized out, I think.  The smart_ptr syntax is
probably the prettiest, but it could be even prettier if a custom class
that omitted the actual pointer support was created.  I'm not sure if
that would be a terribly big win, though.

Aaron W. LaFramboise