> On Jul 31, 2017, at 1:19 AM, Xiaodi Wu <[email protected]> wrote: > > Daryle, this discussion has indeed taken place before. One good place to > start is the Google result for "swift evolution non-conformance".
I added SR-5589, to request a counter protocol to AnyObject. > On Sun, Jul 30, 2017 at 5:30 PM, Daryle Walker via swift-evolution > <[email protected] <mailto:[email protected]>> wrote: > > > On Jul 30, 2017, at 5:03 PM, Tino Heth <[email protected] <mailto:[email protected]>> > > wrote: > > > >> [Apologies if this is in Swift 4 already.] > >> > >> We can have generic parameters match a protocol. But I have an idea in my > >> head that involves the type NOT conforming to a protocol. I don’t think we > >> have a way currently to work with this. > > Why do you want that? > > When something conforms, you know that you can call the methods of the > > protocol, but without conformance, you can't do anything that's not > > possible using "is". > > Also: > > Don't forget retroactive conformance — you can never rely on > > non-conformance. > > I forgot about that last part. But my idea still has merit, due to why I > desired it in the first place. > > The “AnyObject” protocol is marked on all class types. All class types > conform to it, and it’s illegal (as I understand it) to put on a type that > isn’t already a class. I have been working on a “strong type-alias” proposal, > and it has a similar protocol. And I came up with ideas that depend on a type > NOT being a strong type-alias. That’s what prompted the post. Note that these > protocols cannot be retroactively applied, so negation has merit. > > Since there’s a limited number of them, a better solution could be to add a > “NeverAnObject” protocol that’s automatically slapped onto non-class types > (and cannot be added onto class types). And like “AnyObject,” it can be a > base protocol, but this time it forces the conforming protocol to not be for > classes. — Daryle Walker Mac, Internet, and Video Game Junkie darylew AT mac DOT com
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