Simple, Consistent Package Options.
options
Simple, Consistent Package Options
If you've exposed options from a package before, you've inevitably re-written one or more pieces of trivial boilerplate code:
- Prefixing option names with some sort of package namespace
- Building your own option documentation
- Preferentially using a default value, global options or environment variables
- Parsing of environment variables into useful R data
options
aims to make these things easy, without having to copy around boilerplate code.
Quick Start
Defining Options
Define your options using the define_options
shorthand. Interlace descriptions and default values to define multiple options at once.
#' @import options
options::define_options(
"This is an example of how a package author would document their internally
used options. This option could make the package default to executing
quietly.",
quiet = TRUE,
"Multiple options can be defined, providing default values if a global option
or environment variable isn't set.",
second_example = FALSE,
"Default values are lazily evaluated, so you are free to use package functions
without worrying about build-time evaluation order",
lazy_example = fn_not_defined_until_later()
)
When you want more control, you can use define_option
to declare all aspects of how your option behaves.
options::define_option(
option = "concrete_example",
default = TRUE,
desc = paste0(
"Or, if you prefer a more concrete constructor you can define each option ",
"explicitly."
),
option_name = "mypackage_concrete", # define custom option names
envvar_name = "MYPACKAGE_CONCRETE", # and custom environment variable names
envvar_fn = options::envvar_is_true() # and use helpers to handle envvar parsing
)
Documentation
As long as the options have been created as shown above, documenting your options is as easy as adding this small roxygen stub within your package.
#' @eval options::as_roxygen_docs()
NULL
Produces ?mypackage::options
mypackage Options
Description:
Internally used, package-specific options. All options will
prioritize R options() values, and fall back to environment
variables if undefined. If neither the option nor the environment
variable is set, a default value is used.
Options:
quiet
This is an example of how a package author would document their
internally used options. This option could make the package default to
executing quietly.
default:
TRUE
option: mypackage.quiet
envvar: R_MYPACKAGE_QUIET (raw)
...
When your options are used as default values to parameters, you can use the option documentation to populate your function parameter docs.
This is made simple when all of your parameters share the same names as your options.
#' @eval options::as_params()
#' @name options_params
#'
NULL
#' Count to Three
#'
#' @inheritParams option_params
#'
count_to_three <- function(quiet = opt("quiet")) {
for (i in 1:3) if (!quiet) cat(i, "\n")
}
In situations where you have identically named parameters where you don't want to inherit the option documentation, you can provide their names to as_params
to use just a subset of options. You can also reassign documentation for an option to a parameter of a different name.
#' Hello World!
#'
#' @eval options::as_params("silent" = "quiet")
#'
hello <- function(who, silent = opt("quiet")) {
cat(paste0("Hello, ", who, "!"), "\n")
}
Customizing Behaviors
When using define_option
you can set the option_name
and envvar_name
that will be used directly.
But it can be tedious and typo-prone to write these out for each and every option. Instead, you might consider providing a function that sets the default format for your option and environment variable names.
For this, you can use set_option_name_fn
and set_envvar_name_fn
, which each accept a function as an argument. This function accepts two arguments, a package name and internal option name, which it uses to produce and return the corresponding global option name or environment variable name.
options::set_option_name_fn(function(package, name) {
tolower(paste0(package, ".", name))
})
options::set_envvar_name_fn(function(package, name) {
gsub("[^A-Z0-9]", "_", toupper(paste0(package, "_", name)))
})