Use chooseOpsMethod to get Date-IDate correct

Author: MichaelChirico

NAMESPACE

@@ -155,6 +155,7 @@ if (getRversion() >= "3.6.0") {
 export(as.IDate,as.ITime,IDateTime)
 export(second,minute,hour,yday,wday,mday,week,isoweek,isoyear,month,quarter,year,yearmon,yearqtr)
 
+S3method(chooseOpsMethod, IDate)
 S3method("[", ITime)
 S3method("+", IDate)
 S3method("-", IDate)

NEWS.md

@@ -103,6 +103,8 @@
 
 16. `between()` is now more robust with `integer64` arguments. Combining small integer `x` with certain large `integer64` bounds no longer misinterprets the bounds as `double`; if a `double` bound cannot be losslessly converted into `integer64` for comparison with `integer64` `x`, an error is signalled instead of returning a wrong answer with a warning; [#7164](https://github.com/Rdatatable/data.table/issues/7164). Thanks @aitap for the bug report and the fix.
 
+17. `t1 - t2`, where one is an `IDate` and the other is a `Date`, are now consistent with the case where both are `IDate` or both are `Date`, [#4979](https://github.com/Rdatatable/data.table/issues/4749). Thanks @George9000 for the report and @MichaelChirico for the fix.
+
 ### NOTES
 
 1. The following in-progress deprecations have proceeded:

R/IDateTime.R

@@ -91,6 +91,8 @@ round.IDate = function(x, digits=c("weeks", "months", "quarters", "years"), ...)
           years = ISOdate(year(x), 1L, 1L)))
 }
 
+chooseOpsMethod.IDate = function(x, y, mx, my, cl, reverse) inherits(y, "Date")
+
 #Adapted from `+.Date`
 `+.IDate` = function(e1, e2) {
   if (nargs() == 1L)
@@ -115,7 +117,7 @@ round.IDate = function(x, digits=c("weeks", "months", "quarters", "years"), ...)
   if (storage.mode(e1) != "integer")
     internal_error("storage mode of IDate is somehow no longer integer") # nocov
   if (nargs() == 1L)
-    stopf("unary - is not defined for \"IDate\" objects")
+    stopf('unary - is not defined for "IDate" objects')
   if (inherits(e2, "difftime"))
     internal_error("difftime objects may not be subtracted from IDate, but Ops dispatch should have intervened to prevent this") # nocov
 

inst/tests/tests.Rraw

@@ -21566,3 +21566,13 @@ test(2335.3, isoyear(as.IDate("2023-08-15")), 2023L)  # Normal mid-year case
 test(2335.4, isoyear(as.IDate(c("2019-12-30", "2016-01-01", "2023-08-15"))),c(2020L, 2015L, 2023L))
 test(2335.5, isoyear("2019-12-30"), 2020L)
 test(2335.6, isoyear(as.Date("2019-12-30")), 2020L)
+
+# t1-t2 for Date/IDate should be consistent, modulo storage mode #4979
+t1 = as.IDate("2025-07-01")
+t2 = as.IDate("2025-06-01")
+test(2336.1, all.equal(as.Date(t1) - as.Date(t2), t1 - t2))
+test(2336.2, all.equal(as.Date(t2) - as.Date(t1), t2 - t1))
+test(2336.3, all.equal(as.Date(t1) - t2, t1 - t2))
+test(2336.4, all.equal(as.Date(t2) - t1, t2 - t1))
+test(2336.5, all.equal(t1 - as.Date(t2), t1 - t2))
+test(2336.6, all.equal(t2 - as.Date(t1), t2 - t1))