<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">I could read the entire conversation because following the web archives is super unintuitive. So feel free to answer me with a bunch of links if you think my question was already answered.<div class=""><br class=""></div><div class="">Isn't this proposal solving a problem that in practice doesn't exist or isn't common enough to be worth a language level fix? I'm trying to find an example of a common problem - in any language - that would benefit by having final/sealed by default.<br class=""><div class="">
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<br class=""><div><blockquote type="cite" class=""><div class="">On Dec 22, 2015, at 3:22 PM, Greg Parker via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class=""><br class=""><blockquote type="cite" class="">On Dec 22, 2015, at 11:31 AM, Kevin Ballard via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class="">UIKit classes aren't subclassable because of a lack of sealed-by-default, they're subclassable because until very recently there was no way to mark classes as not being subclassable.<br class=""></blockquote><br class="">There are two historical ways to disallow subclassing of public classes.<br class="">1. Perform an isa check in your -init method and halt if it's not your class. Attempts to subclass will get runtime errors.<br class="">2. Mark your class's metaclass symbol as un-exported. Attempts to subclass will get link-time errors.<br class=""><br class="">Both are used but neither is common.<br class=""><br class=""><br class=""><blockquote type="cite" class="">Whether the language has final-by-default/sealed-by-default doesn't really affect this in any way. I guarantee you that once Apple starts putting Swift code in their frameworks, every single framework class Apple releases is going to make an explicit decision about being final/sealed vs inheritable, and the language defaults won't affect that one bit.<br class=""></blockquote><br class="">You may be overestimating Apple's engineers. We're just developers too. Whatever the default is, it will be incorrectly left in place more often than you'd like.<br class=""><br class=""><br class="">-- <br class="">Greg Parker <a href="mailto:gparker@apple.com" class="">gparker@apple.com</a> Runtime Wrangler<br class=""><br class=""><br class="">_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class="">https://lists.swift.org/mailman/listinfo/swift-evolution<br class=""></div></div></blockquote></div><br class=""></div></body></html>