Generic type (see Boost docs)
Basic example showing the use of a vector containing instances of
boost::any, along with the use of any_cast to cast any instances to
source types.
Example using boost::program_options::value_semantic to store values which
can parse a string to the stored value type.
Example using a custom boost::program_options::basic_parsed_options parser
along with an options_description instance to store value types and parse
values from attributes of a pugi::xml_node.