[swift-evolution] Strings in Swift 4

[Nevin Brackett-Rozinsky]

On Sun, Jan 22, 2017 at 6:40 PM, Chris Lattner via swift-evolution <
swift-evolution at swift.org> wrote:

>
> > On Jan 20, 2017, at 9:39 PM, Brent Royal-Gordon via swift-evolution <
> swift-evolution at swift.org> wrote:
> >
> >> On Jan 20, 2017, at 2:45 PM, Dave Abrahams via swift-evolution <
> swift-evolution at swift.org> wrote:
> >>
> >> on Fri Jan 20 2017, Joe Groff <swift-evolution at swift.org> wrote:
> >>
> >>> Jordan points out that the generalized slicing syntax stomps on '...x'
> >>> and 'x...', which would be somewhat obvious candidates for variadic
> >>> splatting if that ever becomes a thing. Now, variadics are a much more
> >>> esoteric feature and slicing is much more important to day-to-day
> >>> programming, so this isn't the end of the world IMO, but it is
> >>> something we'd be giving up.
> >>
> >> Good point, Jordan.
> >
> > In my experiments with introducing one-sided operators in Swift 3, I was
> not able to find a case where you actually wanted to write `c[i...]`.
> Everything I tried needed to use `c[i..<]` instead. My conclusion was that
> there was no possible use for postfix `...`; after all, `c[i...]` means
> `c[i...c.endIndex]`, which means `c[i..<c.index(after: c.endIndex)]`, which
> violates a precondition on `index(after:)`.
>
> Right, the only sensible semantics for a one sided range with an open end
> point is that it goes to the end of the collection.  I see a few different
> potential colors to paint this bikeshed with, all of which would have the
> semantics “c[i..<c.endIndex]”:
>
> 1) Provide "c[i...]":
> 2) Provide "c[i..<]":
> 3) Provide both "c[i..<]” and "c[i…]":
>
> Since all of these operations would have the same behavior, it comes down
> to subjective questions:
>
> a) Do we want redundancy?  IMO, no, which is why #3 is not very desirable.
> b) Which is easier to explain to people?  As you say, "i..< is shorthand
> for i..<endindex” is nice and simple, which leans towards #2.
> c) Which is subjectively nicer looking?  IMO, #1 is much nicer
> typographically.  The ..< formulation looks like symbol soup, particularly
> because most folks would not put a space before ].
>
> There is no obvious winner, but to me, I tend to prefer #1.  What do other
> folks think?
>

I strongly prefer “c[i...]”

Nevin



>
> > If that's the case, you can reserve postfix `...` for future variadics
> features, while using prefix `...` for these one-sided ranges.
>
> I’m personally not very worried about this, the feature doesn’t exist yet
> and there are lots of ways to spell it.  This is something that could and
> probably should deserve a more explicit/heavy syntax for clarity.
>
> -Chris
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