t;T&gt; &gt;
{
    typedef mpl::integral_c_tag tag;
    typedef mpl::int_&lt;object_serializable&gt; type;
    BOOST_STATIC_CONSTANT(
        int,
        value = implementation_level::type::value
    );
};

// nvp objects are generally created on the stack and are never tracked
template&lt;class T&gt;
struct tracking_level&lt;nvp&lt;T&gt; &gt;
{
    typedef mpl::integral_c_tag tag;
    typedef mpl::int_&lt;track_never&gt; type;
    BOOST_STATIC_CONSTANT(
        int, 
        value = tracking_level::type::