ode>int</code> values which are accepted by both <code>equals</code> and <code>hashCode</code>.</p>
<p>If neither <code>equals</code>, <code>hashCode</code>, nor <code>isValidKey</code> is provided,
the default <code>isValidKey</code> instead accepts all values.
The default equality and hashcode operations are assumed to work on all
objects.</p>
<p>Likewise, if <code>equals</code> is <a href="dart-core/identical.html">identical</a>, <code>hashCode</code> is <a href="dart-core/identityHashCode.html">identity