Calculating the difference between two dates in Swift
I ended up creating a custom operator for Date
:
extension Date { static func - (lhs: Date, rhs: Date) -> TimeInterval { return lhs.timeIntervalSinceReferenceDate - rhs.timeIntervalSinceReferenceDate }}
With this operator I can now compute the difference between two dates on a more abstract level without caring about timeIntervalSinceReferenceDate
or what exactly the reference date is – and without losing precision, for example:
let delta = toDate - fromDate
Obviously, I didn't change much, but for me it's a lot more readable and consequent: Swift has the +
operator already implemented for a Date
and a TimeInterval
:
/// Returns a `Date` with a specified amount of time added to it.public static func + (lhs: Date, rhs: TimeInterval) -> Date
So it's already supporting
Date + TimeInterval = Date
Consequently, it should also support
Date - Date = TimeInterval
in my opinion and that's what I added with the simple implementation of the -
operator. Now I can simply write the example function exactly as mentioned in my question:
func computeNewDate(from fromDate: Date, to toDate: Date) -> Date let delta = toDate - fromDate // `Date` - `Date` = `TimeInterval` let today = Date() if delta < 0 { return today } else { return today + delta // `Date` + `TimeInterval` = `Date` }}
It might very well be that this has some downsides that I'm not aware of at this moment and I'd love to hear your thoughts on this.
You can extension with custom operator, and return tuples
extension Date { static func -(recent: Date, previous: Date) -> (month: Int?, day: Int?, hour: Int?, minute: Int?, second: Int?) { let day = Calendar.current.dateComponents([.day], from: previous, to: recent).day let month = Calendar.current.dateComponents([.month], from: previous, to: recent).month let hour = Calendar.current.dateComponents([.hour], from: previous, to: recent).hour let minute = Calendar.current.dateComponents([.minute], from: previous, to: recent).minute let second = Calendar.current.dateComponents([.second], from: previous, to: recent).second return (month: month, day: day, hour: hour, minute: minute, second: second) }}
Using:
let interval = Date() - updatedDateprint(interval.day)print(interval.month)print(interval.hour)
Simply toDate.timeIntervalSince(fromDate)
.
To reimplement your function without adding any extension:
func computeNewDate(from fromDate: Date, to toDate: Date) -> Date { let delta = toDate.timeIntervalSince(fromDate) let today = Date() if delta < 0 { return today } else { return today.addingTimeInterval(delta) }}