xample:</p>
<pre class="language-dart"><code>var set = new Set();
var time1 = new DateTime.fromMillisecondsSinceEpoch(0);
var time2 = new DateTime.fromMillisecondsSinceEpoch(0);
// time1 and time2 are equal, but not identical.
Expect.isTrue(time1 == time2);
Expect.isFalse(identical(time1, time2));
set.add(time1);  // =&gt; true.
// A value equal to time2 exists already in the set, and the call to
// add doesn't change the set.
set.add(time2);  // =&gt; false.
Expect.isTrue(set.length == 1);
Expect.isTrue(id