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Is Argument a Function?

Source: R/assertions.R
assert_function.Rd

Checks if the argument is a function and if all expected arguments are provided by the function.

Usage

assert_function(
  arg,
  params = NULL,
  optional = FALSE,
  arg_name = rlang::caller_arg(arg),
  message = NULL,
  class = "assert_function",
  call = parent.frame()
)

Arguments

arg

A function

The function to be checked

params

A character vector

A character vector of expected argument names for the aforementioned function in arg. If ellipsis, ..., is included in the function formals of the function in arg, this argument, params will be ignored, accepting all values of the character vector.

optional

Is the checked argument optional?

If set to FALSE and arg is NULL then an error is thrown.

arg_name

string indicating the label/symbol of the object being checked.

message

string passed to cli::cli_abort(message). When NULL, default messaging is used (see examples for default messages). "{arg_name}" can be used in messaging.

class

Subclass of the condition.

call

The execution environment of a currently running function, e.g. call = caller_env(). The corresponding function call is retrieved and mentioned in error messages as the source of the error.

You only need to supply call when throwing a condition from a helper function which wouldn't be relevant to mention in the message.

Can also be NULL or a defused function call to respectively not display any call or hard-code a code to display.

For more information about error calls, see Including function calls in error messages.

Value

The function throws an error

  • if the argument is not a function or

  • if the function does not provide all arguments as specified for the params argument (assuming ellipsis is not in function formals)

See also

Checks for valid input and returns warning or errors messages: assert_atomic_vector(), assert_character_scalar(), assert_character_vector(), assert_data_frame(), assert_date_vector(), assert_expr(), assert_expr_list(), assert_filter_cond(), assert_integer_scalar(), assert_list_element(), assert_list_of(), assert_logical_scalar(), assert_named(), assert_numeric_vector(), assert_one_to_one(), assert_param_does_not_exist(), assert_s3_class(), assert_same_type(), assert_symbol(), assert_unit(), assert_vars(), assert_varval_list()

Examples

example_fun <- function(fun) {
  assert_function(fun, params = c("x"))
}

example_fun(mean)

try(example_fun(1))
#> Error in example_fun(1) : 
#>   Argument `fun` must be a function, but is a number.

try(example_fun(sum))
#> Error in example_fun(sum) : 
#>   "x" is not an argument of the function specified for `fun`.