aded if at least
            one of its parameters is a user-defined type. In this case, the <code class="computeroutput"><span class="identifier">double_</span></code> is the 2nd argument to <code class="computeroutput"><span class="keyword">operator</span><span class="special">&gt;&gt;</span></code>,
            and so the proper overload of <code class="computeroutput"><span class="special">&gt;&gt;</span></code>
            is used, converting <code class="computeroutput"><span class="char">','</span></