Merrill Cornish wrote:

Sebastian,

boost::nothing sounds interesting, but I've never run across it before. Where is it defined?

It's a wrong memory on my part. The Boost.Optional library defines boost::none, which is a global instance of boost::none_t. Any optional<T> can be instantiated from a none_t; the resulting object will be empty. http://www.boost.org/libs/optional/doc/optional.html -> Look for the constructor optional<T>::optional( none_t ) Sebastian