POSIXct() mirrors primitive constructors in base R (double(),
character() etc.)
is.POSIXt(x)
is.POSIXlt(x)
is.POSIXct(x)
POSIXct(length = 0L, tz = "UTC")
NA_POSIXct_An object of class POSIXct (inherits from POSIXt) of length 1.
TRUE if x is a POSIXct or POSIXlt object, FALSE otherwise.
is.POSIXt(as.Date("2009-08-03"))
#> [1] FALSE
is.POSIXt(as.POSIXct("2009-08-03"))
#> [1] TRUE