HashCode</a>
and <code>isValidKey</code> is omitted, the resulting set is identity based,
and the <code>isValidKey</code> defaults to accepting all keys.
Such a map can be created directly using <a href="dart-collection/HashSet/HashSet.identity.html">HashSet.identity</a>.</p>
    </section>
    
    <section class="summary source-code" id="source">
      <h2><span>Implementation</span></h2>
      <pre class="language-dart"><code class="language-dart">external factory HashSet(
    {bool equals(E e1, E e2),
 