[boost] [optional] Suggestion for adding an optional_number class

I'd like to make a suggestion for adding an optional class for number types, called optional_number, where the max value of the number type is utilized as the uninitalized value. Differences compared to std::optional: *- No size overhead from the wrapped type* - Theoretically faster (althrough in practice probably negilble) - Can be assigned to any value except the max value - Operator-> is removed as it does not make sense for an integer Notes: - Throws if assigned the numeric_limits<T>::max - Also works with enums, using the underlying_type - The operator bool conversion is missing in the prototype implementation Attaching a prototype implementation (currently for C++14). /Viktor