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

[Max Moiseev]

> On Jun 27, 2017, at 1:03 PM, Adrian Zubarev <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
>>> 
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