[swift-evolution] Feature proposal: Range operator with step

[Xiaodi Wu]

Howard, the point I am raising is that `0...(-9)` is not valid Swift
because the first, "lower" bound is enforced to be less than the second,
"upper" bound.

The problem is that with that restriction certain types of half-open
intervals, namely those where the lower bound is the one being excluded,
cannot be represented as a Range either currently or in Dave A's branch.
On Tue, Apr 5, 2016 at 3:30 PM Howard Lovatt <howard.lovatt at gmail.com>
wrote:

> I much prefer (0 ... -9).by(-1) and  (0 ..< -10).by(-1)
>
> On Wednesday, 6 April 2016, Dave Abrahams via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>>
>> on Tue Apr 05 2016, Xiaodi Wu <xiaodi.wu-AT-gmail.com> wrote:
>>
>> > On Mon, Apr 4, 2016 at 1:22 PM, Dave Abrahams <dabrahams at apple.com>
>> wrote:
>> >>
>> >> on Sat Apr 02 2016, Xiaodi Wu <xiaodi.wu-AT-gmail.com> wrote:
>> >>
>> >>> [snip]
>> >>>
>> >>> Not included:
>> >>> 1. I know Ranges are in flux, so I've held off on extending Range with
>> >>> a striding(by:) method in this proof-of-concept.
>> >>
>> >> They're not in flux, except for not having been reviewed yet; they are
>> >> settled in the swift-3-indexing-model branch.
>> >
>> > Did not know that. Will have to study what's there in more detail.
>> >
>> >>> 2. No attempt at the suggested stride(from:to:steps:) quite yet.
>> >>
>> >> #1 and #2 are mutually exclusive; we prefer #1 as it removes questions
>> >> about the meaning of "to" or "through."
>> >
>> > I wasn't aware that was the thinking. Limiting strides to
>> > `striding(by:)` removes the ability to express `stride(from: 0, to:
>> > -10, by: -1)`
>>
>> IMO this:
>>
>>   (-9...0).reverse()
>>
>> is better than
>>
>>   stride(from: 0, to: -10, by: -1)
>>
>> What do you think?
>>
>> --
>> Dave
>>
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>>
>
>
> --
> -- Howard.
>
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