
</pre>
<!-- @example.prepend('#include <boost/parameter/keyword.hpp>') -->
<!-- @test('compile') -->
<p>It defines a <em>keyword tag type</em> named <tt class="docutils literal"><span class="pre">tag::graph</span></tt> and a <em>keyword
object</em> reference named <tt class="docutils literal">_graph</tt>.</p>
<p>This “fancy dance” involving an unnamed namespace and references
is all done to avoid violating the One Definition Rule (ODR)<a class="footnote-reference" href="#odr" id="id5"><sup>2</sup></a> 