&lt;R&gt;(<wbr>)
    </section>
    <section class="desc markdown">
      <p>Provides a view of this set as a set of <code>R</code> instances.</p>
<p>If this set contains only instances of <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 set (e.g., by using <a href="dart-core/Set/add.html">add</a> or <a href="dart-core/Set/addAll.html">addAll</a>)
must be