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And I have a (unrelated) suggestion for an improvement: add an auxiliary functor for validating. Often there are certain conditions imposed on the options, e.g. a numeric option has to be in some interval or such. This checking can be done once after parsing, but it'd be cleaner to directly incorporate it. One could encode all the information in the type, but that'd be ugly. Using Boost.Lambda, I could imagine a syntax like:

po::checked_value<int> (_1 > 0 && _1 < 5)

instead of

po::value<checked_val<int, bounds_checker<int, 1, 4> > > ()

Sigh. This is on todo list, but I haven't had any time for that.

I forgot to mention that this is especially useful in my case, because then the UI can detect (some) wrong inputs and complain directly. I think one easy way to implement this would be to (1) pass a reference to value_semantic to the validation functions, (2) add a virtual is_correct function to value_semantic that defaults to accepting everything, (3) call value_semantic::is_correct in the validation functions, (4) subclass typed_value to hold a functor that is invoked upon overwritten is_correct, and (5) provide a checked_value function similar to value. (2), (4) and (5) are mostly trivial, and I'm happy to provide you a patch for that. (1) and (3) shouldn't be hard either, but require more invasive changes. - -- - -ness- -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFF/+KlvD/ijq9JWhsRAuOLAJoCWeSVBukRRP+02h2N0bjOxr1PqQCcCtfe B8HQ3EzCP/E6vghOHo0faLI= =pE/C -----END PGP SIGNATURE-----