[R-pkg-devel] More on explosive dependencies

David Hugh-Jones d@vidhughjone@ @ending from gm@il@com
Mon Jul 16 09:58:07 CEST 2018

Hi Russ,

 Possibly relevant: the modelgenerics package (on GitHub) does exactly what
you're suggesting for standard model functions like `nobs` etc. I think at
some point it is going to become part of the tidyverse.


On Mon, 16 Jul 2018 at 02:24, Lenth, Russell V <russell-lenth using uiowa.edu>

> Package developers,
> I posted a question a couple of months ago dealing with how to reduce the
> number of dependencies in a package. Part of the specific issue I face is
> that I have a `cld` S3 method for which the generic is in the multcomp
> package, but I don't want to import multcomp because it comes with a number
> of unneeded dependencies.
> My solution at first appeared to be that I could just export my function
> `cld.emmGrid`; then if users have the multcomp package, this method is
> available. I also moved multcomp from Imports to Suggests, so that it is no
> longer a dependency. This fix works just fine for me. It passed the
> preliminary CRAN checks and it was accepted by CRAN. But then I was advised
> that the package fails the CRAN checks with Debian because those checks
> require S3 methods to actually be registered.
> So what I tried next is what Duncan Murdoch suggested earlier in this
> thread -- to register the method conditionally using the following code in
>     if (requireNamespace("multcomp")) {
>         importFrom(multcomp, cld)
>         S3method(cld, emmGrid)
>     }
> This worked fine in my initial testing, both with multcomp installed and
> with multcomp absent.
> However, now the package doesn't pass the checking procedure. The reason
> apparently is that every package mentioned in import() or importFrom() --
> conditionally or not -- must be listed in Imports in the DESCRIPTION file.
> I could move multcomp back to Imports, but that defeats the whole purpose
> of getting rid of unneeded dependencies. It's a Catch-22.
> Is there any recourse possible? Alas, I'm guessing there isn't, unless we
> can convince everybody to allow unregistered S3 methods on all platforms.
> This situation makes it really difficult for package developers to provide
> methods for other contributors' packages and still keep theirs lightweight.
> Almost all S3 generics are very simple functions, so being forced to load a
> dozen or so namespaces just to register a method is crazy. Plus, the more
> dependencies a package has, the less robust it is to other developers'
> updates.
> I'm now wondering how much interest there is in developing a separate
> package just for generics, say, "S3generics". We could all collaborate to
> contribute our own generics to that one package, move them out of our own
> packages, and instead import just that package.
> Russ
> Russell V. Lenth  -  Professor Emeritus
> Department of Statistics and Actuarial Science
> The University of Iowa  -  Iowa City, IA 52242  USA
> Voice (319)335-0712 (Dept. office)  -  FAX (319)335-3017
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