Skip to contents

Type checks - Objects

predicates-objects.Rd

Functions to test for 'object'-related properties:

  • has_class(): checks if x has a "class" attribute.

  • has_object_bit(): checks if x has the "object" bit set, identical to is.object.

  • has_s4_bit(): checks if x has the "S4" bit set, identical to isS4.

  • is_s4(): checks if x is of type "S4".

  • is_object(): checks if x is of type "object".

  • is_object_like(): checks if object has the "object" bit, while testing for inconsistencies with the other properties above (see 'Details' below).

Usage

has_object_bit()

has_s4_bit()

has_class(x, invalid = "warn", bad = "warn")

is_object_like(x, bad = "warn")

is_s4(x)

is_object(x)

Arguments

x

[any] An object to test.

invalid

["warn" | "false"] How to handle NA or "" values in the class attribute: "warn" to issue a warning and return TRUE; "false" to return FALSE.

bad

["warn" | "false"] How to handle inconsistencies in is_object_like(): "warn" to issue a warning and return if x has a class attribute; "false" to return FALSE.

Value

[TRUE | FALSE] The scalar result of the test.

Details

The relationship between the object-related properties is as follows:

  • class <-> object bit

  • s4 bit -> class/object bit (ideally)

  • s4 typeof -> s4 bit, and -> class/object bit (ideally)

  • object typeof -> class/object bit (ideally)

is_object_like() tests if any of the above are violated.

Examples

xbase <- 1:10
xs3 <- structure(1:10, class = "my_s3")
xs4_int <- methods::setClass("my_s4_int", contains = "integer")(1:10)
xs4_s4 <- methods::setClass("my_s4_s4", slots = c(x = "integer"))(x = 1:10)

# If has class, should have the object bit set, and vice versa:
has_class(xbase) #> FALSE
#> [1] FALSE
has_class(xs3) #> TRUE
#> [1] TRUE
has_object_bit(xs3) #> TRUE
#> [1] TRUE
has_class(xs4_int) #> TRUE
#> [1] TRUE

# S4 objects have the S4 bit set:
has_s4_bit(xs3) #> FALSE
#> [1] FALSE
has_s4_bit(xs4_int) #> TRUE
#> [1] TRUE

# is_s4 test for the typeof() "S4":
typeof(xs4_int) #> "integer"
#> [1] "integer"
is_s4(xs4_int) #> FALSE
#> [1] FALSE
typeof(xs4_s4) #> "S4"
#> [1] "S4"
is_s4(xs4_s4) #> TRUE
#> [1] TRUE

# is_object() test for the typeof() "object", which some OOP systems use,
# and also when an S4 object has its class modified:
suppressWarnings(class(xs4_s4) <- c("new_class", class(xs4_s4)))
typeof(xs4_s4) #> "object"
#> [1] "object"
is_object(xs4_s4) #> TRUE
#> [1] TRUE

# is_object_like() is similar to checking the object bit/existence of a class
# attribute, while cheking for inconsistencies with the other properties:
is_object_like(xbase) #> FALSE
#> [1] FALSE
is_object_like(xs4_int) #> TRUE
#> [1] TRUE

attr(xs4_int, "class") <- NULL
has_s4_bit(xs4_int) #> TRUE (S4 bit is still set)
#> [1] TRUE
is_object_like(xs4_int, bad = FALSE) #> FALSE
#> [1] FALSE

# has_class() is similar, but also checks for NA, "", or duplicate values in
# the class attribute:
class(xs3) <- c("a", "b", "a")
has_class(xs3, invalid = "false") #> FALSE
#> [1] FALSE