If an empty namespace
        sequence is given (that is a macro that expands to nothing), the adapted
        view is placed in the global namespace. If no namespace sequence is given
        (i.e. <code class="computeroutput"><span class="identifier">BOOST_FUSION_ADAPT_STRUCT_NAMED</span></code>),
        the adapted view is placed in the namespace <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fusion</span><span class="special">::