assert_function_expects: Assert function expects specific parameter names

In assertions: Simple Assertions for Beautiful and Customisable Error Messages

Assert function expects specific parameter names

Description

Assert that a function signature includes required set of parameter names in its formal argument list, regardless of whether those parameters have default values. The ... argument is ignored.

Usage

assert_function_expects(
  x,
  required,
  msg = NULL,
  call = rlang::caller_env(),
  arg_name = NULL
)

Arguments

x	a function to check for required parameter names
required	a character vector of parameter names that must appear in the function signature (order does not matter)
msg	The error message thrown if the assertion fails (string)
call	Only relevant when pooling assertions into multi-assertion helper functions. See cli_abort for details.
arg_name	Advanced use only. Name of the argument passed (default: NULL, will automatically extract arg_name).

Value

invisible(TRUE) if function x declares all required parameters, otherwise aborts with the error message specified by msg

Examples

my_fun <- function(x, y = 1, ...) x + y
assert_function_expects(my_fun, c("x", "y"))

try({
  assert_function_expects(my_fun, c("x", "z"))
})

assertions documentation built on Feb. 13, 2026, 5:06 p.m.