cnf

Tools to manage configuration files in R projects.

Examples

Assume you have a configuration file located at ~/.config.R. It may look something like:

~/.config.R

user = "user"
password = "pwd"
...

Now the question is, how do you make these settings available to your R project. cnf provides the following mechanisms:

• register: Register a configuration file. It adds to a list of configurations.
• getcnf: get the value of a config. It is always a list returned with the values in the config as elements.

cnf::register(config = "~/.config.R")
cnf::getcnf("config")

With getcnf we get the config for a given name. You can and should give project specific names to rule out name clashes between them:

cnf::register(
  projA = "pathA/config.R",
  projB = "pathB/config.R"
)

We now have access to these configs using:

cnf::getcnf("projA")
cnf::getcnf("projB")

Note that we can override configurations using this approach; simply by using the same name twice. A warning is raised, however this may be entirely by intention. Consider that you have projects A and B. A has its own configuration and loads it. B depends on A but needs to reconfigure project A. Think of the number of cores, database credentials, and the like. Using this approach we will inherit the configuration but can override what needs to be overridden.

To make this work the order of registering is important. Thus the registration goes into the .onLoad hook of your package. If you do not have a package: you are doomed, go and write a package!

.onLoad <- function(libname, pkgname) {
  cnf::register(
    projA = "pathA/config.R",
    projB = "pathB/config.R",
    maybe = TRUE,
    quiet = TRUE,
    warn = FALSE
  )
}

• maybe allows this call to fail, but will print a message. This is important when we install a package and have no configuration, yet.
• quiet suppresses all warnings and messages.
• warn turns warnings into messages.

Sometimes configurations are stored as R object within the package. As R code and in version control. We can register them preferably as load hook:

.onLoad <- function(libname, pkgname) {
  cnf::register(
    cnf = configObject
  )
}

In this case configObject is a list. We can go wild and provide a fallback/default configuration and allow for override by a file or environment variable:

.onLoad <- function(libname, pkgname) {
  cnf::register(
    config = configObject,
    config = "~/.config.R",
    config = Sys.getenv("CONFIG"),
    maybe = TRUE
  )
}

Using this pattern, we can override the configuration, or parts of it, by an environment variable or config file. The file path in the environment variable has highest priority.

Happy coding…