have been detected if
f's <tt class="docutils literal">age</tt> parameter had been made <tt class="docutils literal">const</tt>, which is always a
good idea whenever possible.  Finally, we recommend that you use
an enclosing namespace for all your code, but particularly for
names with leading underscores.  If we were to leave out the
<tt class="docutils literal">people</tt> namespace above, names in the global namespace
beginning with leading underscores—which are reserved to your C++
compiler—might bec