ernal" href="reference.html#argumentpack"><span class="concept">ArgumentPack</span></a> type, and then use the library's <tt class="docutils literal">value_type&lt; … &gt;</tt>
metafunction to extract “logical parameters”.  <tt class="docutils literal">value_type&lt; … &gt;</tt> is
a lot like <tt class="docutils literal">binding&lt; … &gt;</tt>, but no reference is added to the actual
argument type.  Note that defaults are specified by passing it an
optional third argument:</p>
<pre class="literal