[swift-evolution] [Pitch][Bug?] Test for Anti-Conformance During Generics

[Xiaodi Wu]

Daryle, this discussion has indeed taken place before. One good place to
start is the Google result for "swift evolution non-conformance".

On Sun, Jul 30, 2017 at 5:30 PM, Daryle Walker via swift-evolution <
swift-evolution at swift.org> wrote:

>
> > On Jul 30, 2017, at 5:03 PM, Tino Heth <2th at gmx.de> 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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