:value_type age_type;
  typedef typename boost::property_traits&lt;GPAMap&gt;::value_type gpa_type;

  name_type fred = &quot;Fred&quot;;

  age_type old_age = get(ages, fred);
  gpa_type old_gpa = get(gpas, fred);

  std::cout &lt;&lt; &quot;Fred's old age: &quot; &lt;&lt; old_age &lt;&lt; &quot;\n&quot;
            &lt;&lt; &quot;Fred's old gpa: &quot; &lt;&lt; old_gpa &lt;&lt; &quot;\n&quot;;

  age_type new_age = 18;
  gpa_type new_gpa = 3.9;
  put(ages, fred, new_age);
  put(gpas, fred, new_gpa);
}
</p