[swift-evolution] [Draft] Change @noreturn to unconstructible return type

[Jacob Bandes-Storch]

What about `PreconditionFailure`? If you obtain an instance of this type,
it means a precondition has failed.

Jacob

On Mon, Jun 6, 2016 at 9:48 AM, Joe Groff via swift-evolution <
swift-evolution at swift.org> wrote:

> `Never` seems reasonable to me too. I'll add that to the proposal as an
> alternative.
>
> -Joe
>
> > On Jun 5, 2016, at 11:37 AM, T.J. Usiyan via swift-evolution <
> swift-evolution at swift.org> wrote:
> >
> > I vote for Bottom or Never. None does not convey "this should not occur
> or be evaluated".
> >
> > On Sun, Jun 5, 2016 at 2:26 PM, Антон Жилин <swift-evolution at swift.org>
> wrote:
> > The following names were suggested: NoReturn, Bottom, None, Never.
> > I would pick None, because it looks like opposite to Any and fits nicely
> in generic types.
> >
> > I would prefer the type to be simple, and be implemented as a case-less
> enum (not a bottom value, as in Haskell).
> >
> > None should be a usual enum, with no compiler magic except that
> functions returning None are equivalent to current @noreturn.
> >
> > Example 1.
> > let x: None?
> > // ...
> > let y = x!
> >
> > It will trap in runtime not because we discover scary bottom thing, as
> in Haskell, but because x had value Optional.none at that moment and we
> asserted otherwise.
> > We could prove that it is always true in this case, but compiler must be
> stupid about this.
> >
> > Example 2.
> > Compiler should allow including None in structures. Error will show up
> in constructor, when we will not be able to initialize the field.
> >
> > Example 3.
> > None in an enum case makes that case never appear in values of such a
> type. But compiler can not know about that.
> >
> > - Anton
> >
> > _______________________________________________
> > swift-evolution mailing list
> > swift-evolution at swift.org
> > https://lists.swift.org/mailman/listinfo/swift-evolution
> >
> >
> > _______________________________________________
> > swift-evolution mailing list
> > swift-evolution at swift.org
> > https://lists.swift.org/mailman/listinfo/swift-evolution
>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160606/ac50da43/attachment.html>