> There can't really be an "ImportGenerics", because S3 is so informal. A
> generic function is a function that calls UseMethod, but it can do anything
> else as well. So R would need some fancy code analysis to know whether it
> was safe to import the generic but not all the dependencies of that package,
> and that could change when the package holding the generic was updated.
>
> Examples of generics that do more than simply call UseMethod are rare, but
> they exist: as.data.frame() and sort() are a couple.
>
> Duncan Murdoch
Right -- ImportGenerics was a dumb idea. However, Something like ImportNoDeps
makes sense as an additional category in the DESCRIPTION file. In my example,
if such existed, I could put in the DESCRIPTION file:
ImportNoDeps: multcomp
This would signal that multcomp -- but not necessarily any of its dependencies
-- is required to install emmeans. And in the NAMESPACE file:
importFrom(multcomp, cld)
S3method(cld, emmGrid)
... would import the needed generic and register my new S3 method.
I think this kind of construct could significantly reduce dependencies for
packages that extend other packages' methods.
Russ
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