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

[Joe Groff]

> On Mar 28, 2016, at 5:33 PM, Brent Royal-Gordon <brent at architechies.com> wrote:
> 
>>> Floating-point seconds (as NSTimeIntervals) are the natural Strideable.Stride, but it's not particularly clear to me that you want 1 second to be a default stride. It's the default you would guess, but it's not actually a particularly useful default.
>> 
>> Any fixed-time-period stride with dates is fraught with peril. Not every day is 24 hours, not every minute is 60 seconds, etc. Working with dates requires enough special domain knowledge that I think it'd be harmful to try to genericize numeric concepts over it.
> 
> While this is true, "ten seconds from now" is always ten seconds from now, and "seconds between date1 and date2" is always the same number of seconds. There is a basic level of time measurement and manipulation which is completely independent of time zones and calendars; that's what NSDate and NSTimeInterval represent. They are needed fairly often, and they are perfectly compatible with Strideable's semantics.

Perhaps, but if you make Date strideable by seconds and automatically receive a bunch of utility methods based on that, then it becomes really tempting to abuse absolute time periods, or to accidentally misuse generic Strideable utilities instead of calendar-aware ones. We don't make String a sequence for similar reasons (though perhaps, by analogy to String, there could be `seconds`/`days`/`solarMonths`/`lunarMonths`/etc. views that are Strideable).

-Joe