ertex)
  BOOST_PARAMETER_NAME(index_map)
  BOOST_PARAMETER_NAME(color_map)
}
</pre>
<!-- @test('compile') -->
<p>The declaration of the <tt class="docutils literal">graph</tt> keyword you see here is
equivalent to:</p>
<pre class="literal-block">
namespace graphs
{
  namespace tag { struct graph; } // keyword tag type

  namespace // unnamed
  {
    // A reference to the keyword object
    boost::parameter::keyword&lt;tag::graph&gt;&amp; _graph
    = boost::parameter::keyword&lt;tag::graph&gt;::get();
  }
}