Sets (if create = TRUE) or gets the cache
directory associated with the Require package.
RequireCacheDir(create)
RequirePkgCacheDir(create)A logical indicating whether the path should
be created if it does not exist. Default is FALSE.
If !is.null(getOptionRPackageCache()), i.e., a cache path exists,
the cache directory will be created,
with a README placed in the folder. Otherwise, this function will just
return the path of what the cache directory would be.
To set a different directory than the default, set the system variable:
R_USER_CACHE_DIR = "somePath" and/or R_REQUIRE_PKG_CACHE = "somePath"
e.g., in .Renviron file or Sys.setenv(). See Note below.
Currently, there are 2 different Cache directories used by Require:
RequireCacheDir and RequirePkgCacheDir. The RequirePkgCacheDir
is intended to be a sub-directory of the RequireCacheDir. If you set
Sys.setenv("R_USER_CACHE_DIR" = "somedir"), then both the package cache
and cache dirs will be set, with the package cache a sub-directory. You can, however,
set them independently, if you set "R_USER_CACHE_DIR" and "R_REQUIRE_PKG_CACHE"
environment variable. The package cache can also be set with
options("Require.RPackageCache" = "somedir").