object.
            Views cannot be constructed as separate objects from the container they
            belong to, so the following:
</p>
<pre class="programlisting"><span class="comment">// Wrong: we forgot the &amp; after bm_type::left_type</span>
<span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">left_map</span> <span class="identifier">lm</span> <span class="special">=</span> <span class="identifier">bm</span><span class="special">.</span><span class="identifi