Register S3 methods with @exportS3Method instead of onLoad()

[olivroy]

+ redocument with CRAN roxygen2 and commit left-overs.

Maybe not a good idea after all r-lib/usethis#1923 (comment)

[IndrajeetPatil]

Do you think this comment is still relevant?

[gaborcsardi]

Thanks! What are the pros and cons for this?

[olivroy]

I am not sure. But apparently, since you depend on R 3.6, it can work. From roxygen 7.3.0 blog post, https://roxygen2.r-lib.org/dev/articles/namespace.html#s3

Typically, you will write methods for generics that are either defined in the current package or a package that is a hard dependency2 of your package. Sometimes, however, you will want to write a method for a suggested dependency. In this case, @export will not work because it assumes the generic is included or imported in your NAMESPACE. Instead, use @exportS3Method. This will use “delayed” method registration, which means the method will only be registered when the suggested package is loaded.

To use @exportS3Method you must provide the package and generic name in the following format:

It allows to have a tag in a single place, instead of having to make updates in 2 places.

[olivroy]

I just found the comment I was looking for that advocates for this. r-lib/roxygen2#1534 (comment). Maybe a con is that Suggests problems may arise for circular deps tidyverse/glue#331