[swift-evolution] [Pitch] Introducing the "Unwrap or Die" operator to the standard library

[Jacob Williams]

> On Jun 28, 2017, at 10:13 AM, Tony Allevato <tony.allevato at gmail.com> wrote:
> 
> 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).

I do see your point, and pardon my lack of familiarity with deeper swift capabilities, but would it be possible to restrict the !! operator to @noreturn closures rather than a string and just always throwing a fatalError? This would require the !! operator to have the error type explicitly spelt out, while still honoring the sentiment of !. It would feel more swifty, and you’d get the clarity of knowing that !! is an unsafe operation and you’d know exactly what kind of error is being thrown.

And then ?? could be left as-is and only used for default values.

> 
> On Wed, Jun 28, 2017 at 8:52 AM Jacob Williams via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at 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 at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> 
>>> On Jun 28, 2017, at 8:27 AM, David Hart via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at 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.
>> 
>> 
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