[swift-evolution] [Review] SE-0117: Default classes to be non-subclassable publicly

Károly Lőrentey karoly at lorentey.hu
Sat Jul 9 17:01:38 CDT 2016

> On 2016. Jul 9., at 22:55, Goffredo Marocchi <panajev at gmail.com> wrote:
> Why have they not "fixed" this issue with Java 6/7/8 if it is bad to have the current setup by default? Why C++ x09/x11/x14 is also not making everything sealed/unsubclassable by default?

I'd wager a guess that the strong desire not to break source compatibility with existing code explains why Java and C++ are stuck forever with suboptimal defaults. Some members of this list have a bit of background in C++ language design (understatement of the day!); perhaps they know more.

> Is it possible that having library authors use something like a sealed keyword or similar is good enough for the default case?

Swift is to be safe by default. I believe open subclassability is a power tool that's unsafe without adequate training and thick protective gear; therefore, it is useful to require posting yellow/black hazard signs when it is in use. Safety first.

"Opting for safety sometimes means Swift will feel strict, but we believe that clarity saves time in the long run."


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