Just wanted to throw in my preference for supporting both options. I'd also
like to emphasize that !! isn't appealing just for the sake of terseness, but
also because it completes the ?, ??, !, !! "family" of unwrapping operators in
a way that reinforces their underlying concepts. In that sense, I think the
addition of the operator actually makes the overall system more learnable
through repeated application of a pattern.
Jarod
On Jun 30, 2017, 10:02 -0700, Dave DeLong via swift-evolution
<swift-evolution@swift.org>, wrote:
> These are good points, Brent.
>
>
> > On Jun 29, 2017, at 11:24 PM, Brent Royal-Gordon via swift-evolution
> > <swift-evolution@swift.org> wrote:
> >
> > > On Jun 27, 2017, at 10:16 AM, Erica Sadun via swift-evolution
> > > <swift-evolution@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
> >
> > Finally found a few minutes to read this thread.
> >
> > I'm a big fan of the `Never`-based approach. (I was before, but I am more
> > so now.) Here are the points I can see in its favor:
> >
> > 1. It is extremely clear about what's happening—`!!` is another random
> > operator to learn, but `fatalError(_:)` or `preconditionFailure(_:)` are
> > fairly self-explanatory, and `??` is something you might already be using.
>
> !! is also clear about what’s happening, because it’s just like the existing
> ! operator.
>
> > 2. It allows you to control the optimization behavior by using
> > `fatalError`, `preconditionFailure`, or `assertionFailure` as desired.
>
> Yep. That’s cool.
>
> > 3. If we later change `throw` from being a statement to being a
> > `Never`-returning expression, you could use `throw` on the right-hand side
> > of `??`.
>
> Neat idea. 👍
>
> > 4. It supports other `Never`-returning operations, like `abort()` or
> > `exit(_:)` or your custom `usage()` function, on the right side of `??`.
>
> Yep. That’s cool.
>
> > 5. It supports file-and-line error reporting without having to add any new
> > features; `!!` could not do this because an operator can't have extra,
> > defaulted parameters to carry the file and line.
>
> Erica’s proposal addresses this. Allowing operator functions to accept more
> than 2 parameters that all have default arguments looks like it would be a
> pretty straight-forward and non-controversial change. It would also allow the
> FRP crowd to make their <~ and |> and ಠ_ಠ and (╯°□°)╯︵ ┻━┻ operators all
> capture the #file and #line they’re used on, which would make debugging those
> style of apps much easier.
>
> > 6. It harmonizes with the eventual idea of making `Never` a universal
> > bottom type, but we don't actually have to implement that today, because we
> > can just overload `??` for now.
>
> Yep. That’s cool.
>
> > Against these advantages, the only one I can see for `!!` is that it is
> > terse. Terseness is good, especially for a feature which is competing with
> > the single-character postfix `!` operator, but I can't help but be drawn to
> > the flexibility and power of `??` with a `Never` expression on the
> > right-hand side.
>
> I would argue that terseness is a goal of Swift. If it weren’t, we shouldn’t
> have [Element] as sugar syntax for Array<Element>, or even a bunch of our
> operators (postfix !, postfix ?, overflow checking operators, nil coalescing,
> etc).
>
> IMO, having both !! that takes an error message and ?? that takes a () →
> Never seem like worthwhile goals. The former allows me to be terse, yet still
> expressive, and the latter allows me the customization to do what I want for
> whatever is contextually appropriate in my situation.
>
> I don’t think anyone is arguing that ?? () → Never isn’t useful. The purpose
> of this proposal is to put forward and defend the claim that “!! String” is
> also useful and meets the barrier to entry in to the Standard Library.
>
> Dave
>
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