Efficient swap method for a derived class
<p>Here is a code fragment that speaks for itself. Thank you!</p>

<pre><code>class Foo : private std::vector&lt;int&gt;
{
public:
    void swap(Foo&amp; x)
    {
        std::swap(bar, x.bar);
        // what goes here?
    }
private:
    int bar;
};
</code></pre>
