add {+-}.POSIXt and tests for {+-} POSIXct

NAMESPACE

@@ -1,7 +1,9 @@
 # Generated by roxygen2: do not edit by hand
 
 S3method("+",Date)
+S3method("+",POSIXt)
 S3method("-",Date)
+S3method("-",POSIXt)
 S3method("[<-",hms)
 S3method("[[",hms)
 S3method("units<-",hms)

R/generics.R

@@ -1,10 +1,18 @@
 #' @export
 Ops.hms <- function(e1, e2) {
+  # This logic is hard-coded in R for difftime
+  # cf. https://github.com/wch/r-source/blob/a46559e8f728317da979be60e401899ae60086b2/src/main/eval.c#L3406-L3419
   if (.Generic == "+" && (inherits(e1, "Date") || inherits(e2, "Date"))) {
     return(base::`+.Date`(e1, e2))
   } else if (.Generic == "-" && inherits(e1, "Date")) {
     return(base::`-.Date`(e1, e2))
+  } else if (.Generic == "+" && (inherits(e1, "POSIXt") || inherits(e2, "POSIXt"))) {
+    return(base::`+.POSIXt`(e1, e2))
+  } else if (.Generic == "-" && inherits(e1, "POSIXt")) {
+    return(base::`-.POSIXt`(e1, e2))
   }
+
+  # delegate to Ops.difftime
   res <- NextMethod(.Generic)
   if (inherits(res, "difftime")) {
     as_hms(res)
@@ -18,3 +26,9 @@ Ops.hms <- function(e1, e2) {
 
 #' @export
 `-.Date` <- Ops.hms
+
+#' @export
+`+.POSIXt` <- Ops.hms
+
+#' @export
+`-.POSIXt` <- Ops.hms

tests/testthat/helper-compare.R

@@ -3,9 +3,3 @@ expect_hms_equal <- function(x, y) {
   expect_s3_class(y, "hms")
   expect_equal(as.numeric(x), as.numeric(y))
 }
-
-expect_difftime_equal <- function(x, y) {
-  expect_s3_class(x, "difftime")
-  expect_s3_class(y, "difftime")
-  expect_equal(as.numeric(as_hms(x)), as.numeric(as_hms(y)))
-}

tests/testthat/test-arith.R

@@ -11,11 +11,11 @@ test_that("arithmetics work", {
   expect_equal(hms(days = 1) + as.Date("2016-03-31"), as.Date("2016-04-01"))
   expect_equal(empty_tz(hms(hours = 1) + as.POSIXct("2016-03-31")), as.POSIXct("2016-03-31 01:00:00"))
 
-  expect_difftime_equal(hms(1) + hms(2), hms(3))
-  expect_difftime_equal(hms(1) - hms(2), hms(-1))
-  expect_difftime_equal(2 * hms(1), hms(2))
-  expect_difftime_equal(hms(hours = 1) / 2, hms(minutes = 30))
-  expect_difftime_equal(-hms(1), hms(-1))
+  expect_hms_equal(hms(1) + hms(2), hms(3))
+  expect_hms_equal(hms(1) - hms(2), hms(-1))
+  expect_hms_equal(2 * hms(1), hms(2))
+  expect_hms_equal(hms(hours = 1) / 2, hms(minutes = 30))
+  expect_hms_equal(-hms(1), hms(-1))
 })
 
 test_that("component extraction work", {

tests/testthat/test-generics.R

@@ -56,10 +56,52 @@ test_that("generic operations work as intended", {
 
   # Can't reproduce this warning because we forced compatibility
   hms_result <- hms_test_vec - date_vec
-  expect_warning({
-    difftime_result <- as_hms(difftime_test_vec - date_vec)
-  }, regexp = "Incompatible methods \\(\"Ops.difftime\", \"-.Date\") for \"-\"")
-  expect_equal(hms_result, difftime_result)
+  expect_warning(
+    difftime_result <- as_hms(difftime_test_vec - date_vec),
+    regexp = "Incompatible methods \\(\"Ops.difftime\", \"-.Date\") for \"-\""
+  )
+  expect_equal(hms_result, difftime_result, info = "hms - Date not equal to difftime - Date")
 
   expect_equal(date_vec - hms_test_vec, date_vec - difftime_test_vec)
+
+  # hms {+-} POSIXt
+  posixct_vec <- as.POSIXct(
+    c("2023-03-26 03:00:00", "2023-10-29 02:00:00", NA_character_, "1970-01-01 00:00:00"),
+    tz = "Europe/Berlin"
+  )
+
+  posix_difftime_result <- posixct_vec + as.difftime(1.0, units = "hours")
+  expect_equal(
+    format(posix_difftime_result, usetz = TRUE),
+    c("2023-03-26 04:00:00 CEST", "2023-10-29 02:00:00 CET", NA_character_, "1970-01-01 01:00:00 CET")
+  )
+  expect_equal(posixct_vec + hms(hours = 1L), posix_difftime_result)
+  expect_equal(hms(hours = 1L) + posixct_vec, posix_difftime_result)
+  expect_equal(as.difftime(1.0, units = "hours") + posixct_vec, posix_difftime_result)
+
+  posix_difftime_result <- posixct_vec - as.difftime(1.0, units = "hours")
+  expect_equal(
+    format(posix_difftime_result, usetz = TRUE),
+    c("2023-03-26 01:00:00 CET", "2023-10-29 01:00:00 CEST", NA, "1969-12-31 23:00:00 CET"),
+    info = "POSIXct - difftime"
+  )
+  expect_equal(posixct_vec - hms(hours = 1L), posix_difftime_result)
+
+  hms_result <- hms(hours = 1L) - posixct_vec
+  expect_warning(
+    difftime_result <- as.difftime(3600.0, units = "secs") - posixct_vec,
+    regexp = "Incompatible methods \\(\"Ops.difftime\", \"-.POSIXt\") for \"-\""
+  )
+  # FIXME this currently returns a different result than difftime - POSIXt.
+  # hms - POSIXt produces a hms
+  # difftime - POSIXt produces a POSIXt
+  expect_equal(
+    as.numeric(hms_result), as.numeric(difftime_result),
+    info = "hms - POSIXt not equal to difftime - POSIXt"
+  )
+  expect_hms_equal(hms_result, new_hms(c(-1679788800.0, -1698534000.0, NA_real_, 7200.0)))
+  expect_equal(
+    difftime_result,
+    as.POSIXct(c(-1679788800.0, -1698534000.0, NA_real_, 7200.0), origin = "1970-01-01", tz = "Europe/Berlin")
+  )
 })