"Sam Partington" wrote:
6. The exists(), is_null() and operator bool() methods fall prey to a well known C++ pitfall. Have a look at Bjorn Karlsson's article, "The Safe Bool Idiom": http://www.artima.com/cppsource/safebool.html.
Looks so. It would be nice to have a common support for this in Boost, though.
I suggested this as an addition to the operators library sometime ago, and patches to the code/docs/tests were applied, but they were later removed. I'll to summarise why.
The first suggestion, which was based on Peters pointer to member function conversion : http://lists.boost.org/MailArchives/boost/msg44416.php (the patches) http://lists.boost.org/MailArchives/boost/msg44529.php
But then Daniel Frey found a problem with the implementation for classes with integral conversion operators of their own. The integral conversion operator was a better match and so the safe-bool conversion was never called :
http://lists.boost.org/MailArchives/boost/msg44894.php
So then we tried an implementation based on using a private integral conversion operator and a public operator bool :
http://lists.boost.org/MailArchives/boost/msg45089.php
This worked well in itself, but caused problems with the type traits is_convertible (sorry, don't seem to be able to find a link to any of those messages).
Finally the whole topic was dropped after a long thread, and the code was removed from the CVS tree. A shame I think though, as there were still several open designs which had possiblities. The end of the discussion is here :
http://aspn.activestate.com/ASPN/Mail/Message/boost/1900317
I'd like to see the solution back in boost, we've been using it here for a couple of years now without problems, and we find it very useful. I'd be willing to put more work into it if there is interest.
Reads like a story. Small utilities don't always get handled in the best way. Perhaps you may propose your as new library (which just happens not to add new files). It would take long but at least this process has clear resolution at the end. /Pavel