I vote for (2). Thats what I would have expected. `start` changing from under you is weird.
> On 21 Jun 2016, at 18:44, Tony Parker via swift-corelibs-dev > <swift-corelibs-dev@swift.org> wrote: > > Hi Greg, > >> On Jun 20, 2016, at 9:04 PM, Greg Titus <g...@omnigroup.com >> <mailto:g...@omnigroup.com>> wrote: >> >> One domain where this happens is project planning back from a fixed end >> date. The most well-known of these would be rocket launches: “T minus 10 >> seconds” is exactly a negative time interval from an end date. >> > > That makes sense. > > Let’s say we added negative interval support to the type. I could see it > working in two ways: > > 1. You initialize with a start and negative duration. After this, the ‘end’ > property becomes what you used for ‘start’ and ‘start’ is adjusted according > to the interval. > 2. We keep the start date to always be what you passed in but allow a > negative value for timeInterval and allow for end to be < start. > > Which of these would be the least confusing? > > - Tony > >> That being said, it’s a fairly uncommon use case and I wouldn’t change the >> API to support it on an equivalent basis with normal forward date intervals. >> A separate specific initializer for it might be useful, though. >> >> - Greg >> >>> On Jun 20, 2016, at 4:12 PM, Tony Parker via swift-corelibs-dev >>> <swift-corelibs-dev@swift.org <mailto:swift-corelibs-dev@swift.org>> wrote: >>> >>> Hi Dave, >>> >>> We had some extensive discussion about this ourselves, but we couldn’t come >>> up with a compelling use case for a negative time interval. Can you >>> describe how you wanted to use it? >>> >>> - Tony >>> >>>> On Jun 17, 2016, at 2:01 PM, Dave Lyon via swift-corelibs-dev >>>> <swift-corelibs-dev@swift.org <mailto:swift-corelibs-dev@swift.org>> wrote: >>>> >>>> In attempting to use the new DateInterval value type to improve some >>>> existing code, I ran in to an issue where DateIntervals cannot be >>>> "reverse" intervals, which is contrary to how TimeInterval works, and >>>> somewhat confusing. >>>> >>>> I would propose that the DateInterval value type should be able to be >>>> properly initialized with any TimeInterval, as a reference date and time >>>> interval are all that is actually required in order to construct a >>>> DateInterval properly. >>>> >>>> The simplest solution might be to change the `startDate:interval:` >>>> initializer to one allows for negative time intervals, such as: >>>> >>>> public init(withInterval: TimeInterval, fromDate: Date) { >>>> self.start = Date(timeInterval: interval, since: fromDate) >>>> self.duration = abs(interval) >>>> } >>>> >>>> I believe in general it is preferable to avoid preconditions that require >>>> a subset of a given input type (in this case, that TimeInterval be >>>> positive or 0), and would prefer to see an API where invalid values are >>>> properly converted from the given input to the documented output. E.g. the >>>> old “Be generous with input, strict with output” idea. >>>> >>>> I hope this is the right place to bring this up, but if not I’m happy to >>>> move the conversation to Radar or elsewhere. >>>> >>>> Thanks! >>>> >>>> _______________________________________________ >>>> swift-corelibs-dev mailing list >>>> swift-corelibs-dev@swift.org <mailto:swift-corelibs-dev@swift.org> >>>> https://lists.swift.org/mailman/listinfo/swift-corelibs-dev >>>> <https://lists.swift.org/mailman/listinfo/swift-corelibs-dev> >>> >>> _______________________________________________ >>> swift-corelibs-dev mailing list >>> swift-corelibs-dev@swift.org <mailto:swift-corelibs-dev@swift.org> >>> https://lists.swift.org/mailman/listinfo/swift-corelibs-dev >>> <https://lists.swift.org/mailman/listinfo/swift-corelibs-dev> >> > > _______________________________________________ > swift-corelibs-dev mailing list > swift-corelibs-dev@swift.org > https://lists.swift.org/mailman/listinfo/swift-corelibs-dev
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