 &quot;Nathaniel&quot;]
attendees.formUnion(visitors)
print(attendees)
// Prints &quot;[&quot;Diana&quot;, &quot;Nathaniel&quot;, &quot;Bethany&quot;, &quot;Alicia&quot;, &quot;Marcia&quot;]&quot;
</code></pre>
<p>If the set already contains one or more elements that are also in
<code>other</code>, the existing members are kept.</p>
<pre><code class="language-swift">var initialIndices = Set(0..&lt;5)
initialIndices.formUnion([2, 3, 6, 7])
print(initialIndices)
// Prints &quot;[2, 4, 6, 7, 0, 1, 3]&quot;
</c