[swift-evolution] [Returned for revision] SE-0117: Default classes to be non-subclassable publicly

[Chris Lattner]

> On Jul 14, 2016, at 10:58 PM, Charles Srstka <cocoadev at charlessoft.com> wrote:
> 
>> On Jul 14, 2016, at 4:39 PM, Chris Lattner via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> - Second is that clients of some other public API vended by a non-Apple framework (e.g. a SwiftPM package) may end up in a situation where the framework author didn’t consider subclass-ability, but the client desires it.  In this situation, the core team feels that a bigger problem happened: the vendor of the framework did not completely consider the use cases of the framework.  This might have happened due to the framework not using sufficient black box unit testing, a failure of the imagination of the designer in terms of use cases, or because they have a bug in their framework that needs unanticipated subclass-ability in order to “get a job done”.
> 
> Or because the framework was developed in the real world, rather than Elysium, and real-world framework developers just about *never* anticipate every single way someone might use their framework (Indeed, if developers were capable of such a thing, there would be no need for third-party software in the first place).

I’m not sure what you’re trying to say.  I agree that it is clearly the case that a framework author cannot anticipate every single use case of their framework.  

However, it is just as clearly the case that “unanticipated subclassability” isn’t a general solution to that problem.

-Chris

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