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

[Dave Abrahams]

on Tue Apr 05 2016, Xiaodi Wu <swift-evolution at swift.org> wrote:

> Certainly, for integer literals and strides of -1.
>
> I meant more generally that removal of stride(...) will eliminate the
> possibility of striding to but not through arbitrary half-open intervals (a, b],
> where a < b, by a negative increment, because there is no such thing as `a>..b`
> to express such an interval as a Swift range.
> Of course, all such cases can be handled by adjusting the endpoint and using a
> closed range instead
>

Indeed, if b - a is a multiple of s,

   (a+s...b).striding(by: s).reversed

works.  

The question is whether this case is important enough to create a
special family of functions for, and then deal with the naming issues
raised by
https://github.com/apple/swift-evolution/blob/master/proposals/0051-stride-semantics.md
?

> On Tue, Apr 5, 2016 at 2:54 PM Dave Abrahams
> <dabrahams at apple.com> 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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-- 
Dave