<div dir="ltr"><div class="gmail_default" style="font-family:georgia,serif">I was trying to implement a final class to conform NSCopying by extension. List&lt;T&gt; was a class in Realm object database.</div><div class="gmail_default" style="font-family:georgia,serif"><br></div><div class="gmail_default" style="font-family:georgia,serif">final class List&lt;T&gt; </div><div class="gmail_default" style="font-family:georgia,serif"><br></div><div class="gmail_default" style="font-family:georgia,serif">My implementation:</div><div class="gmail_default" style="font-family:georgia,serif"><br></div><div class="gmail_default" style="font-family:georgia,serif">extension List:NSCopying {</div><div class="gmail_default" style="font-family:georgia,serif">    public func copy(with zone: NSZone? = nil) -&gt; Any {</div><div class="gmail_default" style="font-family:georgia,serif">        ...</div><div class="gmail_default" style="font-family:georgia,serif">    }</div><div class="gmail_default" style="font-family:georgia,serif">}</div><div class="gmail_default" style="font-family:georgia,serif"><br></div><div class="gmail_default" style="font-family:georgia,serif">I got an error called &quot;@objc is not supported within extensions of generic classes.&quot;. Any idea why there is a limitation of this? Thanks.</div><div class="gmail_default" style="font-family:georgia,serif"><br></div><div class="gmail_default" style="font-family:georgia,serif">Zhaoxin</div></div>