otential value, or error,
that will be available at some time in the future.
Receivers of a <a href="dart-async/Future-class.html">Future</a> can register callbacks
that handle the value or error once it is available.
For example:</p>
<pre class="language-dart"><code>Future&lt;int&gt; future = getFuture();
future.then((value) =&gt; handleValue(value))
      .catchError((error) =&gt; handleError(error));
</code></pre>
<p>A <a href="dart-async/Future-class.html">Future</a> can be completed in two ways:
with a