Compatibility:</strong></span> This trait is provided
        for completeness, since it's part of the Technical Report on C++ Library
        Extensions. However, there is currently no way to portably implement this
        trait. The default version provided always inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>,
        and has to be explicitly specialized for types with virtual destructors unless
        the compiler used has compiler <a class="link" 