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

[Erica Sadun]

I'll give this a kick around as soon as I get a moment and revise. I am slightly concerned that we discussed variations of this in the past (throwing if memory serves, with `Error` on the rhs) and that it broke the expectations of nil-coalescing. 

In general, does everyone prefer `?? () -> Never` or `!! () -> Never`? I can argue both ways, with the goal in reading code as "unwrap or die".

-- E

> On Jun 27, 2017, at 7:16 PM, Max Moiseev via swift-evolution <swift-evolution at swift.org> wrote:
> 
> The compatibility testing revealed no related errors. And the full test suite only shows one that I listed already.
> 
> Max
> 
> 
>> On Jun 27, 2017, at 3:28 PM, Xiaodi Wu <xiaodi.wu at gmail.com <mailto:xiaodi.wu at gmail.com>> wrote:
>> 
>> This solution is nifty indeed, and has the chief advantage of working.
>> On Tue, Jun 27, 2017 at 16:55 Max Moiseev via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> On Jun 27, 2017, at 1:03 PM, Adrian Zubarev <adrian.zubarev at devandartist.com <mailto:adrian.zubarev at devandartist.com>> wrote:
>>> 
>>> How about?
>>> 
>>> public func ?? <T>(optional: T?, noreturnOrError: @autoclosure () throws -> Never) rethrows -> T {
>>>     switch optional {
>>>     case .some(let value):
>>>         return value
>>>     case .none:
>>>         try noreturnOrError()
>>>     }
>>> }
>>> 
>> 
>> Yeah, I saw your email right after I sent mine =)
>> This works, I tried it and also ran the test suite. There was only one error.
>> 
>>   var s: String = ns ?? "str" as String as String // expected-error{{cannot convert value of type 'NSString?' to expected argument type 'String?'}}
>>                                                                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>                                                                      cannot convert value of type 'String' to expected argument type 'NSString'
>> 
>> 
>> I now wonder what the effect on the source compatibility suite would be:
>> https://github.com/apple/swift/pull/10639 <https://github.com/apple/swift/pull/10639>
>> 
>> 
>> Max
>> 
>>> 
>>> 
>>> -- 
>>> Adrian Zubarev
>>> Sent with Airmail
>>> 
>>> Am 27. Juni 2017 um 21:54:57, Max Moiseev via swift-evolution (swift-evolution at swift.org <mailto:swift-evolution at swift.org>) schrieb:
>>> 
>>>> 
>>>>> On Jun 27, 2017, at 10:38 AM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>> 
>>>>> As you write, this operator becomes sugar for “?? fatalError()” once Never becomes a true bottom type.
>>>>> 
>>>>> In the meantime, can’t the same thing be accomplished by overloading fatalError so it’s a generic function that returns a discardable result of type T, which in turn calls the Never-returning overload?
>>>> 
>>>> I like this idea more than adding an extra operator, but overloading fatalError won’t work now because of https://github.com/apple/swift/blob/master/stdlib/public/core/Optional.swift#L668 <https://github.com/apple/swift/blob/master/stdlib/public/core/Optional.swift#L668>
>>>> 
>>>> 
>>>> 
>>>> 
>>>>> On Tue, Jun 27, 2017 at 12:25 Erica Sadun via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>> Using an operator to provide feedback on the context of a failed unwrap has become a commonly implemented approach in the Swift developer Community. What are your thoughts about adopting this widely-used operator into the standard library?
>>>>> 
>>>>> guard !lastItem.isEmpty else { return }
>>>>> let lastItem = array.last !! "Array must be non-empty"
>>>>> 
>>>>> Details here:  https://gist.github.com/erica/423e4b1c63b95c4c90338cdff4939a9b <https://gist.github.com/erica/423e4b1c63b95c4c90338cdff4939a9b>
>>>>> 
>>>>> Thank you for your thoughtful feedback, -- E
>>>>> 
>>>>> _______________________________________________
>>>>> swift-evolution mailing list
>>>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>>>> _______________________________________________
>>>>> swift-evolution mailing list
>>>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>>> 
>>>> _______________________________________________
>>>> swift-evolution mailing list
>>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>> 
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-evolution <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/20170628/76875172/attachment.html>