[R-pkg-devel] Extending an S3 method, but putting the package in Suggests?

[David Hugh-Jones]

Thank you for this info and the suggestion!
David

On Tue, 14 Mar 2017 at 09:06, Martin Maechler <maechler at stat.math.ethz.ch>
wrote:

> >>>>> David Hugh-Jones <davidhughjones at gmail.com>
> >>>>>     on Tue, 14 Mar 2017 02:46:35 +0000 writes:
> >>>>> David Hugh-Jones <davidhughjones at gmail.com>
> >>>>>     on Tue, 14 Mar 2017 02:46:35 +0000 writes:
>
>     > Hi,
>     > Cross-posted from SO:
>     >
> http://stackoverflow.com/questions/42776058/extending-an-s3-generic-from-an-optional-package
>
>   ((sent my answer there as well))
>
>     > I have a package which provides an as.FlexTable method for its
> objects,
>     > extending the S3 generic from the ReporteRs package. So, my
> NAMESPACE file,
>     > generated by roxygen, has lines:
>
>     > importFrom(ReporteRs,as.FlexTable)
>     > ...
>     > S3method(as.FlexTable,huxtable)
>     > ...
>     > export(as.FlexTable)
>
>     > I don't much want to put ReporteRs in Imports: in the DESCRIPTION
> file,
>     > because it involves a big external dependency on Java. But, when I
> put it
>     > into Suggests:, R CMD check gives me errors like "Namespace
> dependency not
>     > required".
>
>     > Is there anyway I can extend the generic without making a hard
> dependency?
>
> No.  Importing is a hard dependency..
> Some people do not import formally but use  '<pkgNamespace>::<obj>'
> instead, *and* conditionalize their code on the availability of
> that namespace.
> I don't recommend that at all, and particularly not for
> extending a generic.
>
> I recommend you talk with the maintainer of 'ReporteRs':
> 1) You could use a common (yet-to-create) very small package say
> 'flexS3generics'
>    which provides S3 generics (and S4 if ..) you want to use
>    both, and then both you and her/him import from that mini package.
>    You'd be both authors of that package.
>
> 2) If your package is much smaller (in its footprint, incl
>    dependencies) than 'ReporteRs' she/he may agree to import the
>    S3 generic from your package instead of the other way around.
>
> Both are clean solutions,
> and both need some time-coordination when releasing to CRAN,
> '1)' being easier: Once the 'flexS3generics' is released to
> CRAN, change (both) your package(s) to
> importFrom(flexS3generics,*) but these changes and CRAN
> submissions are then independent of each other.
>
>
>     > Cheers,
>     > David
>
> --
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