ng zero sized empty base classes, or
          </li>
<li class="listitem">
            the compiler providing <a class="link" href="../intrinsics.html" title="Support for Compiler Intrinsics">intrinsics</a>
            to detect empty classes - this latter case can be tested for by checking
            to see if the macro BOOST_IS_EMPTY is defined.
          </li>
</ul></div>
<p>
        Can not be used with incomplete types.
      </p>
<p>
        Can not be used with union types, until is_union can be mad