port for variadic macros
        auto can be used to avoid repeating the type. <code class="literal">set_expr<span class="emphasis"><em>N</em></span></code>
        is the expression that is invoked to set the <span class="emphasis"><em>N</em></span>th element
        of an instance of <code class="computeroutput"><span class="identifier">type_name</span></code>.
        This expression may access variables named <code class="computeroutput"><span class="identifier">obj</span></code>
        of type <code c