#include <boost/parameter.hpp>

namespace foo {

    BOOST_PARAMETER_NAME(arg1)
    BOOST_PARAMETER_NAME(arg2)

    template <class Tag>
    struct base {
        template <class ArgPack>
        base(ArgPack const & args) 
        : val1(args[_arg1])
        , val2(args[_arg2])
        {}

        int val1,val2;
    };

    template <class Tag>
    struct derived : base<Tag> {
        BOOST_PARAMETER_CONSTRUCTOR(
            derived, (base<Tag>), tag,
            (optional (arg1,int,1) (arg2,int,2)))
    };

} /* foo */

struct default_ {};

int main(int argc, char * arg[]) {
    foo::derived<default_> instance();
    return 0;
}