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

[Erica Sadun]

> On Mar 29, 2016, at 11:26 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
> 
> On Tue, Mar 29, 2016 at 7:48 PM, Dave Abrahams <dabrahams at apple.com <mailto:dabrahams at apple.com>> wrote:
>> 
>> on Tue Mar 29 2016, Xiaodi Wu <xiaodi.wu-AT-gmail.com> wrote:
>> 
>>> Relatedly, while you're tackling this big revision:
>>> 
>>> I've tried to play around with what it would take to write a generic
>>> non-error-accumulating striding method, and afaict, it would be
>>> enormously cleaner if Strideable types are guaranteed to have + and *
>>> (well, Strideable.Stride needs *, to be more accurate),
>> 
>> That should happen automatically, since it conforms to SignedNumber,
>> when we get the Integer protocols updated (project currently on hold while
>> we land this other revision).
>> 
>>> since the iterator needs to be able to compute end = start + iteration
>>> * stride.
>> 
>> Don't you need division too if you're going to do this?
> 
> I didn't seem to ever need division. See attached playground (which
> borrows shamelessly from existing code and Erica's proposal, and which
> is written in Swift 2.2 because that's what I had handy).

Have you considered trying to extend the `swift-3-indexing-model <https://github.com/apple/swift/tree/swift-3-indexing-model>` branch
at the Swift repo to take the floating point approach into account? Dave A
is working on a massive overhaul of ranges (including `Countable` items
and one would presume floating point closed and open intervals as well), 
and I'd love to see better implementations of, for example,  `(x..<y).striding(by:z)`
happen for Double types.

I'd be happy to throw a proposal together based on a proof of concept,
if you had the flexibility to work on the coding.

-- Erica

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