vignettes/assertive-programming.Rmd
assertive-programming.RmdAssertive programming follows the principles of fail fast and fail visibly. It is implemented by issuing an informative error message if the function arguments fail to satisfy specific criteria. This is particularly important in R because it is a dynamically typed language.
There are a host of R packages to facilitate assertive programming. Here I am interested in those packages that are
The most useful packages that I am aware of that satisfy these criteria are
This vignette consists of an overview of each package followed by a comparison.
In short the checkr package is recommended over the alternatives if you are looking for a set of expressive, light-weight, pipe-friendly assertive functions with customizable object names.
The base package offers the stopifnot() function.
height <- dplyr::starwars$height
stopifnot(is.character(height))
#> Error: is.character(height) is not TRUEThe error message is not that helpful if the user doesn’t know what is.character() tests for.
In a function it behaves as follows:
my_fun <- function(x) stopifnot(is.character(x))
my_fun(height)
#> Error in my_fun(height): is.character(x) is not TRUEThe assertthat package offers assert_that().
library(assertthat)
assert_that(is.character(height))
#> Error: height is not a character vectorThe error message is a big improvement on stopifnot()’s.
In a function it behaves as follows:
my_fun <- function(x) assert_that(is.character(x))
my_fun(dplyr::starwars$height)
#> Error: x is not a character vectorPerhaps the neatest feature is the ability to set your own error message for an assertion function using on_failure().
is.character2 <- function(x) is.character(x)
on_failure(is.character2) <- function(call, env) {
paste0(deparse(call$x), " must be a character - sort it out!")
}
assert_that(is.character2(height))
#> Error: height must be a character - sort it out!The checkmate package provides a plethora of functions to check the type and related properties of common objects.
library(checkmate)
assert_character(height)
#> Error in eval(expr, envir, enclos): Assertion on 'height' failed: Must be of type 'character', not 'integer'.In a function it behaves as follows
my_fun <- function(x) assert_character(x)
my_fun(height)
#> Error in my_fun(height): Assertion on 'x' failed: Must be of type 'character', not 'integer'.In addition, the assert() function allows multiple alternative check** functions (those which return a string of the error message on failure and a TRUE on success) to be combined into one assertion.
assert(checkCharacter(height), checkFactor(height))
#> Error: Assertion failed. One of the following must apply:
#> * checkCharacter(height): Must be of type 'character', not 'integer'
#> * checkFactor(height): Must be of type 'factor', not 'integer'The checkr package provides a set of expressive functions to test the values of objects.
library(checkr)
check_vector(height, "")
#> Warning: `check_vector()` was deprecated in checkr 0.5.1.
#> Please use chk::chk_vector(), chk::check_dim(), chk::chk_unique(), chk::chk_sorted(), chk::chk_named(), and/or chk::check_values() instead.
#> Error: height must be class characterIn a function it behaves as follows:
my_fun <- function(x) check_vector(x, "")
my_fun(height)
#> Warning: `check_vector()` was deprecated in checkr 0.5.1.
#> Please use chk::chk_vector(), chk::check_dim(), chk::chk_unique(), chk::chk_sorted(), chk::chk_named(), and/or chk::check_values() instead.
#> Error: x must be class characterAnd multiple alternative checks can be combined using the checkor() function.
checkor(check_vector(height, ""), check_vector(height, 1))
#> Warning: `checkor()` was deprecated in checkr 0.5.1.
#> Please use `chk::chkor()` instead.
#> Warning: `check_vector()` was deprecated in checkr 0.5.1.
#> Please use chk::chk_vector(), chk::check_dim(), chk::chk_unique(), chk::chk_sorted(), chk::chk_named(), and/or chk::check_values() instead.
#> Warning: `check_vector()` was deprecated in checkr 0.5.1.
#> Please use chk::chk_vector(), chk::check_dim(), chk::chk_unique(), chk::chk_sorted(), chk::chk_named(), and/or chk::check_values() instead.
#> Error: height must be class character OR height must be class numericIf all checks are passed stopifnot() returns an invisible NULL, while assert_that() returns TRUE. In contrast, checkmate::assert_** and checkr::check_** return a copy of the original object which allows them to be used in pipes.
Although there is no way to customize the error message produced by stopifnot(), assert_that() allows the programmer to specify the message for a individual test using the msg argument. In the case of checkmate and checkr the programmer can specify the variable name using the .var.name and x_name argument, respectively. This can be very helpful in functions.
my_fun <- function(x) check_vector(x, "", x_name = substitute(x))
my_fun(height)
#> Warning: `check_vector()` was deprecated in checkr 0.5.1.
#> Please use chk::chk_vector(), chk::check_dim(), chk::chk_unique(), chk::chk_sorted(), chk::chk_named(), and/or chk::check_values() instead.
#> Error: height must be class character