here's another possibility:
value<type>(&variable, "filename")->......
something like that was in the pre-review version, with the difference that the value name was also used to specify flags, e.g "filename?" would mean the value is optional.
Yes ... I like this best.
Also, I'm not sure why 0-argument items couldn't appear in a config file. I declare the number of arguments used by options before I parse the config file, after all.
Because the current config parser, systantically, requires that everything specified there has a value. If you specify that an option accepts no explicit value, it can't be present in config file.
OK, your statement was with reference to the current config parser ;) A newer parser could recognize the end of an option name first, then interrogate the option to see if it takes an argument, then if it does, expect to parse a "= value".