[swift-evolution] Subclass Existentials

[Jordan Rose]

> On Feb 1, 2017, at 15:17, David Hart <david at hartbit.com> wrote:
> 
> 
> On 2 Feb 2017, at 00:06, Jordan Rose <jordan_rose at apple.com <mailto:jordan_rose at apple.com>> wrote:
> 
>> I agree with Chris on both counts. Either we need to continue to import ‘NSFoo <NSBar> *’ as ‘NSFoo’ in the Swift 4 compiler’s “Swift 3 compatibility mode”, or we need to come up with all the cases where a normally-unsound conversion needs to be permitted (possibly with a warning) in order to avoid breaking existing programs. The latter is technically doable, but would be much more work, which would likely hurt the proposal’s chances of getting into Swift 4.
> 
> I don't know what you think, but I don't see much advantage in importing it as NSFoo & NSBar is Swift 3 compatibility mode. I wouldn't mind it being a Swift 4 mode only of the importer.
> 
> Correct?

That’s my thinking too. I’d (we’d) just like to see it called out more explicitly in the proposal. :-) You could list the other approach as “alternatives considered”, even if it was only briefly considered, or you could just leave it out.

Jordan

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