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

[Xiaodi Wu]

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> wrote:

> 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
>
>
> Max
>
>
>
> --
> Adrian Zubarev
> Sent with Airmail
>
> Am 27. Juni 2017 um 21:54:57, Max Moiseev via swift-evolution (
> swift-evolution at swift.org) schrieb:
>
>
> On Jun 27, 2017, at 10:38 AM, Xiaodi Wu via swift-evolution <
> 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
>
>
>
>
> On Tue, Jun 27, 2017 at 12:25 Erica Sadun via swift-evolution <
> 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
>>
>> Thank you for your thoughtful feedback, -- E
>>
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