Implement Set Operations methods for Dates

[DanChaltiel]

Hi,

Using set operations like setdiff on dates removes the date class.

Here is a reprex with a very naive workaround:

library(lubridate)  
a = seq(as_date(1), as_date(10), by=1) 
b = seq(as_date(5), as_date(10), by=1) 

setdiff(a, b)  
#> [1] 1 2 3 4

setdiff.Date = function(x, y) base::setdiff(x, y) |> as_date()
setdiff(a, b)
#> [1] "1970-01-02" "1970-01-03" "1970-01-04" "1970-01-05"

^{Created on 2024-02-06 with reprex v2.0.2}

Of course, the same problem and solution happen for other set operations like intersect and others.

I guess that since they are implemented for the Interval class, it would make sense to implement them for Date. I'm not using other lubridate classes much but maybe they have the same problem.