Is an Argument a Character Scalar (String)?

Checks if an argument is a character scalar and (optionally) whether it matches one of the provided values.

assert_character_scalar(
  arg,
  values = NULL,
  case_sensitive = TRUE,
  optional = FALSE,
  arg_name = rlang::caller_arg(arg),
  message = NULL,
  class = "assert_character_scalar",
  call = parent.frame()
)

Arguments

arg

A function argument to be checked

Default value

none

values

A character vector of valid values for arg. Values is converted to a lower case vector if case_sensitive = FALSE is used.

Default value

NULL

case_sensitive

Should the argument be handled case-sensitive? If set to FALSE, the argument is converted to lower case for checking the permitted values and returning the argument.

Default value

TRUE

optional

Is the checked argument optional? If set to FALSE and arg is NULL then an error is thrown

Default value

FALSE

arg_name

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

Default value

rlang::caller_arg(arg)

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.

Default value

NULL

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 arg is not a character vector or if arg is a character vector but of length > 1 or if its value is not one of the values specified. Otherwise, the input is returned invisibly.

See also

Checks for valid input and returns warning or errors messages: assert_atomic_vector(), assert_character_vector(), assert_data_frame(), assert_date_vector(), assert_expr(), assert_expr_list(), assert_filter_cond(), assert_function(), 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(msg_type) {
  assert_character_scalar(msg_type, values = c("warning", "error"))
}

example_fun("warning")

try(example_fun("message"))
#> Error in example_fun("message") : 
#>   Argument `msg_type` must be equal to one of "warning" or "error".

try(example_fun(TRUE))
#> Error in example_fun(TRUE) : 
#>   Argument `msg_type` must be a scalar of class <character>, but is
#> `TRUE`.

# handling arguments case-insensitive
example_fun2 <- function(msg_type) {
  msg_type <- assert_character_scalar(
    msg_type,
    values = c("warning", "error"),
    case_sensitive = FALSE
  )
  if (msg_type == "warning") {
    print("A warning was requested.")
  }
}

example_fun2("Warning")
#> [1] "A warning was requested."