Process package attributes

process_attributes() processes C level comment attributes. It automates a number of tasks, such as:

• Generation of a src/init.c file. This includes:

  • Exporting C functions to the R side through the .Call and .External mechanisms.

  • Registering C callables for use by other packages.

• Optional generation of a pair of package API files in inst/include/<pkg.c> and inst/include/<pkg.h> for the public callables registered in the init.c file.

process_attributes() determines the functions to include in the init.c file through the use of C comments placed directly above the function of interest and formatted like // [[ export() ]]. See the sections below for a complete description.

process_attributes(path = ".", debug = FALSE)

Arguments

path	[character(1)] The relative file path to the top level of your package.
debug	[logical(1)] Should the lines that will be used to construct the init.c and API files be returned as a named list of character vectors rather than written to disk?

Value

A named list of 3 elements: init, api_c, and api_h. These contain the lines written to their corresponding file. If debug = FALSE, this is returned invisibly. If debug = TRUE, it is returned visibly and the lines are not written to file.

Export

Export a C function to the R side as a CallRoutine, suitable for use with .Call().

// [[ export(name = NA_character_) ]]

• name: [character(1)]

  A character string with no spaces in the name. Used to override the name that is generated for the R routine object. The default uses the name of the exported C function as the name for the R routine.

Export External / External2

Export a C function to the R side as an ExternalRoutine, suitable for use with .External() or .External2().

// [[ export_external(n, name = NA_character_) ]]
// [[ export_external2(n, name = NA_character_) ]]

• n: [integer(1)]

  The number of arguments expected when calling this routine from the R side. Meaning that if you have a routine called pkg_my_fun that you plan to call like .External(pkg_my_fn, arg1, arg2), then you should pass n = 2.

• name: [character(1)]

  A character string with no spaces in the name. Used to override the name that is generated for the R routine object. The default uses the name of the exported C function as the name for the R routine.

Callable

Register a C function to be callable by other R packages.

// [[ callable(name = NA_character_, hidden = FALSE) ]]

• name: [character(1)]

  A character string with no spaces in the name. Used to override the name that is generated for the callable object. The default uses the name of the exported C function as the name for the callable.

• hidden: [logical(1)]

  A logical. Should the registered callable also get an entry in the API files created in ./inst/include/? The default includes it in the API. Flipping to hidden = TRUE registers the callable with R_RegisterCCallable() but does not generate an API entry for it, meaning that it can only be retrieved by another package's C code by using R_GetCCallable().

Init

Sometimes you need to initialize extra objects at package load time. By marking a function with init(), it will get included at the end of the call to R_init_<pkg>(), which is called whenever the package is loaded. The function marked with init() should return void and take 1 argument, a DllInfo*, typically given the variable name dll.

// [[ init() ]]