  guaranteed to contain legal values and will throw an exception when
          this guarantee is violated. In other words, we automatically get
          checking of input variables with no additional programming.</p></li>
<li class="listitem"><p>On calling of the function <code class="computeroutput">f</code>, arguments of type
          <code class="computeroutput">input_safe_t</code> are converted to values of type
          <code class="computeroutput">safe_t</code> . In this particular example, it can