Skip to contents

Create an assertion function

Source: R/assert_create.R
assert_create.Rd

This function creates an assertion function that can be used to check the validity of an input. All assertions provided with this package are created using either assert_create() or assert_create_chain()

Usage

assert_create(func, default_error_msg = NULL)

Arguments

func

A function defining the assertion criteria. This function should return a logical value (TRUE when assertion is passed or FALSE when it fails). Alternatively, instead of returning FALSE, you can return a string which will act as the error message. In this latter case, you don't need to supply a default_error_msg

default_error_msg

A character string providing an error message in case the assertion fails. Must be supplied if function func returns FALSE when assertion fails (as opposed to a string) Can include the following special terms

  1. {arg_name} to refer to the name of the variable supplied to the assertion.

  2. {arg_value} to refer to the value of the variable supplied to the assertion

  3. {code_to_evaluate} to evaluate the code within the error message. Replace code_to_evaluate with your code

  4. {.strong bold_text} to perform inline formatting. Replace bold_text with your text. See cli documentation for details

Value

An assertion function.

Examples

#' # Create an assertion function that checks that a character string is all
# lower case
assert_character <- assert_create(
  is.character,
  "{arg_name} must be a character vector, not a {class(arg_value)}"
)

# Use the assertion function
try({
is_lower("hello") # Returns invisible TRUE
is_lower("Hello") # Aborts the function with the error message
})
#> Error in is_lower("hello") : could not find function "is_lower"