checkFunction: Check if an argument is a function

In checkmate: Fast and Versatile Argument Checks

Check if an argument is a function

Description

Check if an argument is a function

Usage

checkFunction(x, args = NULL, ordered = FALSE, nargs = NULL, null.ok = FALSE)

check_function(x, args = NULL, ordered = FALSE, nargs = NULL, null.ok = FALSE)

assertFunction(
  x,
  args = NULL,
  ordered = FALSE,
  nargs = NULL,
  null.ok = FALSE,
  .var.name = vname(x),
  add = NULL
)

assert_function(
  x,
  args = NULL,
  ordered = FALSE,
  nargs = NULL,
  null.ok = FALSE,
  .var.name = vname(x),
  add = NULL
)

testFunction(x, args = NULL, ordered = FALSE, nargs = NULL, null.ok = FALSE)

test_function(x, args = NULL, ordered = FALSE, nargs = NULL, null.ok = FALSE)

expect_function(
  x,
  args = NULL,
  ordered = FALSE,
  nargs = NULL,
  null.ok = FALSE,
  info = NULL,
  label = vname(x)
)

Arguments

x	[any] Object to check.
args	[character] Expected formal arguments. Checks that a function has no arguments if set to character(0). Default is NULL (no check).
ordered	[logical(1)] Flag whether the arguments provided in args must be the first length(args) arguments of the function in the specified order. Default is FALSE.
nargs	[integer(1)] Required number of arguments, without .... Default is NULL (no check).
null.ok	[logical(1)] If set to TRUE, x may also be NULL. In this case only a type check of x is performed, all additional checks are disabled.
.var.name	[character(1)] Name of the checked object to print in assertions. Defaults to the heuristic implemented in vname.
add	[AssertCollection] Collection to store assertion messages. See AssertCollection.
info	[character(1)] Extra information to be included in the message for the testthat reporter. See expect_that.
label	[character(1)] Name of the checked object to print in messages. Defaults to the heuristic implemented in vname.

Value

Depending on the function prefix: If the check is successful, the functions assertFunction/assert_function return x invisibly, whereas checkFunction/check_function and testFunction/test_function return TRUE. If the check is not successful, assertFunction/assert_function throws an error message, testFunction/test_function returns FALSE, and checkFunction/check_function return a string with the error message. The function expect_function always returns an expectation.

See Also

Other basetypes: checkArray(), checkAtomic(), checkAtomicVector(), checkCharacter(), checkComplex(), checkDataFrame(), checkDate(), checkDouble(), checkEnvironment(), checkFactor(), checkFormula(), checkInteger(), checkIntegerish(), checkList(), checkLogical(), checkMatrix(), checkNull(), checkNumeric(), checkPOSIXct(), checkRaw(), checkVector()

Examples

testFunction(mean)
testFunction(mean, args = "x")

checkmate documentation built on Aug. 18, 2025, 5:36 p.m.