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

Joe Groff jgroff at apple.com
Wed Mar 30 11:26:14 CDT 2016

> On Mar 30, 2016, at 8:50 AM, Dave Abrahams <dabrahams at apple.com> wrote:
> on Tue Mar 29 2016, Joe Groff <jgroff-AT-apple.com> wrote:
>>> 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).
> Except that collections aren't Strideable.  A strideable type is a
> value that has an implied unit of measure so that you can offset it
> without reference to any collection.

Who said anything about collections?


More information about the swift-evolution mailing list