Ensure empty constructors return 0-length vectors

Fixes #707

NEWS.md

@@ -4,6 +4,7 @@ Version 1.7.4.9000
 ### NEW FEATURES
 
 * [#713](https://github.com/tidyverse/lubridate/issues/713) `as_datetime()` always returns a `POSIXct()`
+* [#707](https://github.com/tidyverse/lubridate/issues/707) Constructors return 0-length inputs when called with no arguments
 * [#672](https://github.com/tidyverse/lubridate/issues/672) Eliminate all partial argument matches
 * [#695](https://github.com/tidyverse/lubridate/issues/695) Durations can now be compared with numeric vectors.
 * [#681](https://github.com/tidyverse/lubridate/issues/681) New constants `NA_Date_` and `NA_POSIXct_` which parallel built-in primitive constants.

R/durations.r

@@ -243,7 +243,9 @@ setMethod("[[<-", signature(x = "Duration"),
 #' @export
 duration <- function(num = NULL, units = "seconds", ...) {
   nums <- list(...)
-  if (is.character(num)) {
+  if (is.null(num) && missing(...)) {
+    .duration_from_num(numeric(), units)
+  } else if (is.character(num)) {
     as.duration(parse_period(num))
   } else if (!is.null(num) && length(nums) > 0) {
     c(.duration_from_num(num, units), .duration_from_units(nums))

R/intervals.r

@@ -191,14 +191,18 @@ unique.Interval <- function(x, ...) {
 #'
 #' is.interval(period(months= 1, days = 15)) # FALSE
 #' is.interval(interval(ymd(20090801), ymd(20090809))) # TRUE
-interval <- function(start, end = NULL, tzone = tz(start)) {
+interval <- function(start = NULL, end = NULL, tzone = tz(start)) {
 
   if (is.null(tzone)) {
     tzone <- tz(end)
     if (is.null(tzone))
       tzone <- "UTC"
   }
 
+  if (is.null(start) && is.null(end)) {
+    return(new("Interval", numeric(), start = POSIXct(), tzone = "UTC"))
+  }
+
   if (is.character(start) && is.null(end)) {
     return(parse_interval(start, tzone))
   }

R/periods.r

@@ -393,7 +393,12 @@ setMethod("$<-", signature(x = "Period"), function(x, name, value) {
 #' @export
 period <- function(num = NULL, units = "second", ...) {
   nums <- list(...)
-  if (is.character(num)) {
+  if (is.null(num) && missing(...)) {
+    new("Period", numeric(),
+      year = numeric(), month = numeric(), day = numeric(),
+      hour = numeric(), minute = numeric()
+    )
+  } else if (is.character(num)) {
     parse_period(num)
   } else if (!is.null(num) && length(nums) > 0) {
     c(.period_from_num(num, units), .period_from_units(nums))

tests/testthat/test-durations.R

@@ -1,5 +1,11 @@
 context("Durations")
 
+test_that("duration() returns zero-length vector", {
+  x <- duration()
+  expect_s4_class(x, "Duration")
+  expect_length(x, 0)
+})
+
 test_that("duration constructor doesn't accept non-numeric or non-character inputs", {
   expect_error(duration(interval(ymd("2014-01-01"), ymd("2015-01-01"))))
 })

tests/testthat/test-intervals.R

@@ -1,5 +1,11 @@
 context("Intervals")
 
+test_that("interval() returns zero-length vector", {
+  x <- interval()
+  expect_s4_class(x, "Interval")
+  expect_length(x, 0)
+})
+
 test_that("is.interval works as expected", {
   expect_false(is.interval(234))
   expect_false(is.interval(as.POSIXct("2008-08-03 13:01:59", tz = "UTC")))

tests/testthat/test-periods.R

@@ -1,5 +1,11 @@
 context("Periods")
 
+test_that("period() returns zero-length vector", {
+  x <- period()
+  expect_s4_class(x, "Period")
+  expect_length(x, 0)
+})
+
 test_that("period constructor doesn't accept non-numeric or non-character inputs", {
   expect_error(period(interval(ymd("2014-01-01"), ymd("2015-01-01"))))
 })