code>R</code>, all read operations
will work correctly. If any operation tries to access an element
that is not an instance of <code>R</code>, the access will throw instead.</p>
<p>Elements added to the queue (e.g., by using <a href="dart-collection/ListQueue/addFirst.html">addFirst</a> or <a href="dart-collection/ListQueue/addAll.html">addAll</a>)
must be instance of <code>R</code> to be valid arguments to the adding function,
and they must be instances of <code>E</code> as well to be accepted by
this queu