[Rd] Correct use of tools::R_user_dir() in packages?

[Carl Boettiger]

tools::R_user_dir() provides configurable directories for R packages
to write persistent information consistent with standard best
practices relative to each supported operating systems for
applications to store data, config, and cache information
respectively.  These standard best practices include writing to
directories in the users home filespace, which is also specifically
against CRAN policy.

These defaults can be overridden by setting the environmental
variables R_USER_DATA_DIR , R_USER_CONFIG_DIR, R_USER_CACHE_DIR,
respectively.

If R developers should be using the locations provided by
tools::R_user_dir() in packages, why does CRAN's check procedure not
set these three environmental variables to CRAN compliant location by
default (e.g. tempdir())?

In order to comply with CRAN policy, a package developer can obviously
set these environmental variables themselves within the call for every
example, every unit test, and every vignette.  Is this the recommended
approach or is there a better technique?

Thanks for any clarification!

Regards,

Carl

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Carl Boettiger
http://carlboettiger.info/