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

[David Hart]

> On 27 Jun 2017, at 20:23, Dave DeLong via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Also a +1 from me. This is something I always put in to my code.
> 
> I agree that having `Never` as a bottom type is interesting, but even if that were the case, the proposed “!!” operator is still useful, because it short-circuits having to fatalError() myself. IE:
> 
> let last = array.last ?? fatalError(“array must not be empty”)

The above solution with Never is the better solution IMHO:

No new operator
More flexible: what if you want something else than a fatalError? For example, I might want to define a logAndFatalError() function which stores the error to a log file before trapping.

> vs
> 
> let last = array.last !! “Array must not be empty"
> 
> I also think having it “fatalError” in shipping code is fine, because it’s equivalent to what would happen if you incorrect force-unwrap.
> 
> Dave
> 
>> On Jun 27, 2017, at 12:08 PM, Zach Waldowski via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> Big +1.
>> 
>> Using `!` is widely seen as a smell. However, the need for it still arises; they are preconditions, of a sort. It has become prevalent in my teams’ codebases to do “guard else preconditionFailure”.
>> 
>> I like `!!` over something like `?!`; it follows the pattern that almost every `?` in the language has an equivalent `!`.
>> 
>> The implementation details are ultimately not relevant to me. I’m a fan of `Never` being a bottom type for more reasons than just this. I also see no reason why operator funcs couldn’t accept file and line as extra arguments on the rhs.
>> 
>> Best,
>>   Zachary Waldowski
>>   zach at waldowski.me <mailto:zach at waldowski.me>
>> 
>> On Tue, Jun 27, 2017, at 01:16 PM, Erica Sadun via swift-evolution 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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