Dart: Invalid override
<p>The following code:</p>

<pre><code>abstract class Foo {
  List&lt;Object&gt; get c;

  Foo update(List c);
}

class Bar extends Foo {
  final List&lt;int&gt; c;

  Bar(this.c);

  Bar update(List&lt;int&gt; l) =&gt; new Bar(l);
}
</code></pre>

<p>generates the message:</p>

<pre><code>ERROR: Invalid override. The type of DA.update ((List&lt;Date&gt;) → DA) is not
       a subtype of Attribute.update ((List&lt;dynamic&gt;) → Attribute).
</code></pre>

<p>I'm using version 1.16.0-dev.5.1.</p>

<p>Is this correct?  I thought a subclass is a subtype.</p>