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> 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!
>
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