Hi,
I'm developing a package whose API is only meant to be used in other
packages via imports or pkg::foo(). There should be no need to attach
this package so that its API appears on the search() path. As a
maintainer, I want to avoid having it appear in search() conflicts by
mistake.
This means that, for instance, other packages should declare this
package under 'Imports' or 'Suggests' but never under 'Depends'. I
can document this and hope that's how it's going to be used. But, I'd
like to make it explicit that this API should be used via imports or
::. One approach I've considered is:
.onAttach <- function(libname, pkgname) {
if (nzchar(Sys.getenv("R_CMD"))) return()
stop("Package ", sQuote(pkgname), " must not be attached")
}
This would produce an error if the package is attached. It's
conditioned on the environment variable 'R_CMD' set by R itself
whenever 'R CMD ...' runs. This is done to avoid errors in 'R CMD
INSTALL' and 'R CMD check' "load tests", which formally are *attach*
tests. The above approach passes all the tests and checks I'm aware
of and on all platforms.
Before I ping the CRAN team explicitly, does anyone know whether this
is a valid approach? Do you know if there are alternatives for
asserting that a package is never attached. Maybe this is more
philosophical where the package "contract" is such that all packages
should be attachable and, if not, then it's not a valid R package.
This is a non-critical topic but if it can be done it would be useful.
Thanks,
Henrik
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