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

Dave Abrahams dabrahams at apple.com
Wed Mar 30 13:42:32 CDT 2016

on Wed Mar 30 2016, Joe Groff <jgroff-AT-apple.com> wrote:

>> 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?

That's what those views are.


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