(ArgumentPack const&amp; args)
{
    std::cout &lt;&lt; &quot;index = &quot; &lt;&lt; args[_index] &lt;&lt; std::endl;
    return 0;
}

int x = print_index(_index = 3);  // prints &quot;index = 3&quot;
</pre>
<!-- @example.prepend('''
#include <boost/parameter.hpp>
#include <iostream>''') -->
<p>Also, <span class="concept">ArgumentPack</span>s can be composed using the comma operator.
The extra parentheses below are used to prevent the compiler from
seeing two separate arguments to <tt class="docutils liter