[swift-evolution] Strings in Swift 4

[Nevin Brackett-Rozinsky]

>
> Are there contexts in which we would want i... and i..< to do different
> things?


I posit that in the context of incomplete ranges, we always want “i...” to
mean “greater than or equal to i”, and we do not want “i..<” to mean
anything.

We may, however, want something like “i<..” to mean “strictly greater than
i”, though I’m not sure how it should be spelled.

Nevin


On Mon, Jan 30, 2017 at 12:31 PM, Nate Cook via swift-evolution <
swift-evolution at swift.org> wrote:

>
> > On Jan 30, 2017, at 8:51 AM, Thorsten Seitz via swift-evolution <
> swift-evolution at swift.org> wrote:
> >
> >> Am 23.01.2017 um 02:14 schrieb James Froggatt via swift-evolution <
> swift-evolution at swift.org>:
> >>
> >> Could we add subscript labels to the list of options? While keeping the
> range syntax is appealing, I'm concerned it may cause confusion if the
> operators are used out of context.
> >
> > Good point!
> >
> >> The wording is up for debate, but something like this should be a fair
> alternative:
> >> items[from: i]
> >> items[upTo: i]
> >
> > For me that's at least as readable as the range syntax.
> >
> >>
> >> Sorry if this has been covered elsewhere (can't find the answer in this
> thread), but my first questions on discovering these operators (my source
> of confusion) would be what happens if I try the following:
> >> let partialRange = 0..< //is this an infinite range?
> >> let x = items[partialRange] //shouldn't this cause an out of bounds
> error?
> >
> > Good point! Probably this shouldn't be allowed, making the literal range
> syntax with open ends tied into the subscript which is a bit confusing
> indeed.
>
> `partialRange` here is an incomplete range, not an infinite one. When you
> use an incomplete range to subscript a collection, the collection
> "completes" it by filling in the start or end index as required. You can
> see more about the details of incomplete ranges in this proposal:
> https://github.com/apple/swift-evolution/blob/master/
> proposals/0132-sequence-end-ops.md
>
> One other aspect of incomplete ranges that I haven't seen discussed
> (though I may have missed it) is how they work inpattern matching. It would
> be nice to use incomplete ranges in switch statements, so that instead of:
>
>     switch x {
>     case let y where y < 0: print("< 0")
>     case 0...10: print("0-10")
>     case let y where y > 10: print("> 10")
>     default: print("wat")
>     }
>
> we could write:
>
>     switch x {
>     case ..<0: print("< 0")
>     case 0...10: print("0-10")
>     case 10...: print("> 10")
>     default: print("wat")
>     }
>
> To me, that implies that we'll want a postfix ... operator to exist,
> though I agree it's not clear what it should do in a subscript. Are there
> contexts in which we would want i... and i..< to do different things?
>
> Nate
>
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