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

[Jaden Geller]

> On Jun 29, 2017, at 7:35 PM, Yuta Koshizawa <koher at koherent.org> wrote:
> 
> "In -Ounchecked builds, the optimizer may assume that this function is never called. Failure to satisfy that assumption is a serious programming error.”
> 
> Yes, and so the following `!!` can perform identically to `!` in -Ounchecked builds when it is inlined.

Yes, I guess I wasn’t clear. I mean that there’s no problem.

> public static func !!(optional: Optional, errorMessage:
> @autoclosure () -> String) -> Wrapped {
>     precondition(optional != nil, errorMessage())
>     return optional!
> }
> 
> --
> Yuta
> 
> 
> 2017-06-29 6:42 GMT+09:00 Jaden Geller <jaden.geller at gmail.com <mailto:jaden.geller at gmail.com>>:
> 
> > On Jun 28, 2017, at 7:47 AM, Erica Sadun via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> >
> >
> >> On Jun 28, 2017, at 3:52 AM, Yuta Koshizawa via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> >>
> >> Hi, I think it is an orthogonal issue if we need a new operator. It is
> >> also possible to introduce an infix `!` for it.
> >>
> >> I am sure that we do not need to avoid `precondition` as long as we
> >> use it appropriately. It is useful to realize consistent behavior with
> >> `Array`'s `subscript`, forced unwrapping `!`, `&+` and so on. In this
> >> context, `precondition` does not mean a general word "precondition"
> >> but the `precondition` function in the Swift standard library, which
> >> is removed when -Ounchecked.
> >
> >
> > How would the line run then? Would it simply act as a forced unwrapped under -Ounchecked?
> 
> From the docs:
> 
> "In -Ounchecked builds, the optimizer may assume that this function is never called. Failure to satisfy that assumption is a serious programming error.”
> 
> Aka, v. bad things happen if the precondition does not hold.
> 
> >
> > -- E
> >
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> 
> 

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