single integer which represents the state of the object
that affects <a href="dart-core/Duration/operator_equals.html">operator ==</a> comparisons.</p>
<p>All objects have hash codes.
The default hash code represents only the identity of the object,
the same way as the default <a href="dart-core/Duration/operator_equals.html">operator ==</a> implementation only considers objects
equal if they are identical (see <a href="dart-core/identityHashCode.html">identityHashCode</a>).</p>
<p>If <a href="dart-core/Dur