Hi, Recently when using the Boost Program options library, I was surprised to find that I was unable to pass a boost.optional object to store supplied options in. For example; namespace bpo = boost::program_options; boost::optional<std::string> opt_str; bpo::options_description desc("Allowed options"); desc.add_options() ("help", "produce help message") ("opt", bpo::value(&opt_str), "Something optional") // Store value of 'opt' in 'opt_str' ; What I expected to happen would be that 'opt_str' would be valid if 'opt' is supplied by the user, and not valid otherwise. However, the above code causes a compile error deep within lexical_cast because, of course, performing such an operation on a boost.optional doesn't make sense. The attached patch to Program Options rectifies the issue by filtering out optional objects within before calling lexical_cast, but to be honest, I'm not sure if this is the correct approach or if this is even a desirable feature. I like the idea of setting an optional object this way instead of testing the variables_map later on, but perhaps there's something I am missing or a better way to accomplish the same thing. Please have a look and let me know your thoughts. Thanks, -- chris