  Instead,
we'll give them generic names and use the special type
<tt class="docutils literal"><span class="pre">boost::parameter::void_</span></tt> as a default:</p>
<pre class="literal-block">
namespace boost { namespace python {

template &lt;
    class A0
  , class A1 = parameter::void_
  , class A2 = parameter::void_
  , class A3 = parameter::void_
&gt;
struct class_
{
    <em>…</em>
};

}}
</pre>
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