her iterator-like
          type (the <code class="computeroutput"><span class="identifier">Base</span></code> <a name="base1"></a>_ type) while modifying just a few aspects of the underlying
          type's behavior is an extremely common one, and it's the pattern addressed
          by <code class="computeroutput"><span class="identifier">iterator_adaptor</span></code>. Using
          <code class="computeroutput"><span class="identifier">iterator_adaptor</span></code> is very
          much like using <