title: Dart how to declare growable list of list
body: <p>I want to initialize a growable list of lists. Both the outer list and all the inner lists should be growable. I tried the following but they they don't work.</p>
  
  <pre><code>List&lt;List&lt;String&gt;&gt; fixturesOfLeagues = List&lt;List&lt;String&gt;&gt;();
  List&lt;List&lt;String&gt;&gt; fixturesOfLeagues = [];
  List&lt;List&lt;String&gt;&gt; fixturesOfLeagues = [[]];
  </code></pre>
  
  <p>Any idea how to do it?</p>