Hi,
I am developing a package B that, among other things, also offers some
extra S3-methods for functions in package A if the user has installed A.
I do not want to list A under Depends of B, as the dependency list of A
is rather long, and most potential users of B will not be interested in
package A. Unfortunately I struggle with doing this right. So far I have
listed A under Suggests, and had a .onLoad function in B with
if (require(A)) registerS3methods(newMethodsMatrix, package = A, env =
environment(B))
But starting with R 2.13 or R 2.14, R CMD check complain about this
require call in .onLoad, referring to the "good practice"-section of
.onAttach. I guess this could also be a problem when uploading the
package to CRAN, so I am trying to find another solution.
So far I have tried:
List A under Suggest of B, with a conditional import in NAMESPACE.
If I build a Windows-binary from this when A is installed, this package
can be installed but not loaded on computers where A is not installed.
List A under Enhances of B.
This seems to be the right thing, as the R extensions manual says: "the
‘Enhances’ field lists packages “enhanced” by the package at hand, e.g.,
by providing methods for classes from these packages".
However, although it seems I can install and load package B when I
conditionally import package A in the NAMESPACE, R CMD check stops with
the error: Namespace dependency not required: A
If I remove the import, R CMD check is happier, but I cannot load the
package after installing.
I have read about the use of "Suggest", "Enhances" etc in "Writing R
Extensions", but could not figure out the right way to do this. I am
sure there is something I am missing here.
Thanks,
Jon
--
Jon Olav Skøien
Joint Research Centre - European Commission
Institute for Environment and Sustainability (IES)
Land Resource Management Unit
Via Fermi 2749, TP 440, I-21027 Ispra (VA), ITALY
jon.sko...@jrc.ec.europa.eu
Tel: +39 0332 789206
Disclaimer: Views expressed in this email are those of the individual and do
not necessarily represent official views of the European Commission.
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