> On Jun 28, 2017, at 10:44 AM, Adrian Zubarev via swift-evolution > <swift-evolution@swift.org> wrote: > > Well the main debate is that, we all want early access to a feature that will > be part of Swift as soon as `Never` becomes the bottom type. When this > happens the `??` will automatically support the pitched behavior. Until then > if we all agree that we should add it now in a way that will not break > anything we can simply add an overload to `??` as I previously showed. >
I believe we should add it now, but I like the recent observation that making ?? suddenly become a potentially crashing operator violates the expectation that ? is an indication of safety. On the other hand, the existing semantics of Swift are that ! is always dangerous, so making !! be the a potentially crashing operator is much more consistent with the language. > There is no need for `!!` because it will fade in the future. If you think of > `Never` as a bottom type now then `??` will already make total sense. The > default value for T from rhs might be T or Never. I respectfully disagree with your absolute position on this topic. Even with Never as a bottom type in the future, it would still be more convenient for me to type: let last = array.last !! “Array must be non-empty" … than it ever would be to type: let last = array.last ?? fatalError(“Array must be non-empty”) Dave > > @erica: the rhs argument should be called something like `noreturnOrError` > and not `defaultValue`. And we should keep in mind that when Never becomes > the bottom type we have to remove that overload from stdlib, because > otherwise it will be ambiguous. > > --- > > On the other hand if we tackle a different operator then we should rething > the 'default value operator' because the second ? signals an optional but not > a non-optional or an inplicit unwrapped operator. In that case I personally > thing ?! would make more sense. Unwrap or (non-optional | IUO | trap/die) > > -- > Adrian Zubarev > Sent with Airmail > Am 28. Juni 2017 um 18:13:18, Tony Allevato via swift-evolution > (swift-evolution@swift.org <mailto:swift-evolution@swift.org>) schrieb: > >> It's hard for me to articulate, but "foo !! message" feels a little too much >> like a Perl-ism for my taste. Objectively that's not a great criticism on >> its own, but I just don't like the "smell" of an operator that takes a value >> on one side and a string for error reporting purposes on the other. It >> doesn't feel like it fits the style of Swift. I prefer a version that makes >> the call to fatalError (and thus, any other non-returning handler) >> explicitly written out in code. >> >> So, if the language can already support this with ?? and autoclosure/Never >> as was shown above, I'd rather see that added to the language instead of a >> new operator that does the same thing (and is actually less general). >> >> On Wed, Jun 28, 2017 at 8:52 AM Jacob Williams via swift-evolution >> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >> I feel that the !! operator would be necessary for indicating that if this >> fails then something went horribly wrong somewhere and we should throw the >> fatalError. This allows the inclusion of optimizations using -Ounchecked and >> is clear that this is an operation that could result in a runtime error just >> like force unwrapping. >> >> If we want code clarity and uniformity, then I think !! Is much better than >> ?? because it goes right along with the single ! Used for force unwrapping. >> However, this does depend on if the operator would be returning some kind of >> error that would cause the program to exit. >> >> I think the ?? operator should not cause a program to exit early. It goes >> against optional unwrapping principles. I think code could get very >> confusing if some ? would return nil/a default value, and others would be >> causing your program to crash and exit. The ? operators should always be >> classified as safe operations. >> >>> On Jun 28, 2017, at 9:41 AM, Ben Cohen via swift-evolution >>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >>> >>> >>>> On Jun 28, 2017, at 8:27 AM, David Hart via swift-evolution >>>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >>>> >>>> Count me in as a strong proponent of ?? () -> Never. We don't need to >>>> burden the language with an extra operator just for that. >>> >>> You could say the same about ?? >>> >>> The concern that an additional operator (and one that, IMO, fits well into >>> existing patterns) is so burdensome seems way overweighted in this >>> discussion IMO. >>> >>> Adding the operator, and encouraging its use, will help foster better >>> understanding of optionals and legitimate use of force-unwrapping in a way >>> that I don’t think `?? fatalError` could. >>> >>> >>> _______________________________________________ >>> swift-evolution mailing list >>> swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>> https://lists.swift.org/mailman/listinfo/swift-evolution >>> <https://lists.swift.org/mailman/listinfo/swift-evolution> >> >> _______________________________________________ >> swift-evolution mailing list >> swift-evolution@swift.org <mailto:swift-evolution@swift.org> >> https://lists.swift.org/mailman/listinfo/swift-evolution >> <https://lists.swift.org/mailman/listinfo/swift-evolution> >> _______________________________________________ >> swift-evolution mailing list >> swift-evolution@swift.org >> https://lists.swift.org/mailman/listinfo/swift-evolution > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution
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