<div dir="ltr">What about `PreconditionFailure`? If you obtain an instance of this type, it means a precondition has failed.<div class="gmail_extra"><br clear="all"><div><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div>Jacob<br></div></div></div></div>
<br><div class="gmail_quote">On Mon, Jun 6, 2016 at 9:48 AM, Joe Groff via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">`Never` seems reasonable to me too. I'll add that to the proposal as an alternative.<br>
<br>
-Joe<br>
<div class="HOEnZb"><div class="h5"><br>
> On Jun 5, 2016, at 11:37 AM, T.J. Usiyan via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br>
><br>
> I vote for Bottom or Never. None does not convey "this should not occur or be evaluated".<br>
><br>
> On Sun, Jun 5, 2016 at 2:26 PM, Антон Жилин <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br>
> The following names were suggested: NoReturn, Bottom, None, Never.<br>
> I would pick None, because it looks like opposite to Any and fits nicely in generic types.<br>
><br>
> I would prefer the type to be simple, and be implemented as a case-less enum (not a bottom value, as in Haskell).<br>
><br>
> None should be a usual enum, with no compiler magic except that functions returning None are equivalent to current @noreturn.<br>
><br>
> Example 1.<br>
> let x: None?<br>
> // ...<br>
> let y = x!<br>
><br>
> 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.<br>
> We could prove that it is always true in this case, but compiler must be stupid about this.<br>
><br>
> Example 2.<br>
> Compiler should allow including None in structures. Error will show up in constructor, when we will not be able to initialize the field.<br>
><br>
> Example 3.<br>
> None in an enum case makes that case never appear in values of such a type. But compiler can not know about that.<br>
><br>
> - Anton<br>
><br>
> _______________________________________________<br>
> swift-evolution mailing list<br>
> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
><br>
><br>
> _______________________________________________<br>
> swift-evolution mailing list<br>
> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
<br>
_______________________________________________<br>
swift-evolution mailing list<br>
<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
</div></div></blockquote></div><br></div></div>