Assert input is a function — assert_function • assertions

Assert input is a function

Usage

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

Arguments

x: An object
msg: A character string containing the error message to display if x is not a function
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 x is a function, otherwise aborts with the error message specified by msg

Examples

try({
# Assert that a variable is a function
x <- function(a, b) { a + b }
assert_function(x)  # does nothing

# Assert that a variable is not a function
x <- "not a function"
assert_function(x)  # stops execution and prints an error message
})
#> Error in eval(expr, envir) : 
#>   'x' must be a function, not a character