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

[Xiaodi Wu]

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)` because Range enforces (and it looks like it will
continue to do so in the swift-3-indexing-model branch?) `lowerBound
<= upperBound`, and in a half-open range it's the upper bound that's
excluded.

>> 2. No tests written yet for this proof-of-concept; I noticed that
>> there's a stub for testing strides with bounds of type Double, but
>> there's a comment about things not being ready because Double conforms
>> to RandomIndexType--not sure what to make of that.
>
> Comments in that branch are badly out-of-date.  It's worth trying that,
> especially since there is no RandomAccessIndexType in that branch any
> longer.
>
>> 3. Haven't gotten around to testing performance.