[R-pkg-devel] unregistered S3 methods in a package

[John Fox]

Thanks Toby and Jeff for chiming in on this.

Jeff: I already read Kurt Hornik's post on "S3 Method Lookup" and quite 
a few other sources.

The main point is that failing to register the methods works in that the 
methods are nevertheless invoked internally by functions in the package 
but don't shadow versions of the methods registered by other package 
externally (e.g., at the command prompt), which was the effect that I 
wanted. Moreover, as I said, R CMD check (unlike roxygen) didn't complain.

As I mentioned, this is now moot for the cv package, but I'm still 
interested in the answer, as, apparently, is Toby.

Best,
  John

On 2024-09-04 5:12 p.m., Jeff Newmiller wrote:
> Caution: External email.
> 
> 
> I have been reluctant to pipe up on this because I am no expert on the dark corners of the S3 dispatch mechanism, but I think unregistered S3 methods in packages are verboten. Perhaps [1] will shed some light?
> 
> [1] https://blog.r-project.org/2019/08/19/s3-method-lookup/
> 
> On September 4, 2024 11:21:22 AM PDT, Toby Hocking <tdhock5 using gmail.com> wrote:
>> I got this warning too, so I filed an issue to ask
>> https://github.com/r-lib/roxygen2/issues/1654
>>
>> On Mon, Sep 2, 2024 at 2:58 PM John Fox <jfox using mcmaster.ca> wrote:
>>>
>>> As it turned out, I was able to avoid redefining coef.merMod(), etc., by
>>> making a simple modification to the cv package.
>>>
>>> I'm still curious about whether it's OK to have unregistered S3 methods
>>> for internal use in a package even though that's no longer necessary for
>>> the cv package.
>>>
>>> On 2024-09-02 11:34 a.m., John Fox wrote:
>>>> Caution: External email.
>>>>
>>>>
>>>> Dear R-package-devel list members,
>>>>
>>>> I want to introduce several unregistered S3 methods into the cv package
>>>> (code at <https://github.com/gmonette/cv>). These methods have the form
>>>>
>>>>          coef.merMod <- function(object, ...) lme4::fixef(object)
>>>>
>>>> The object is to mask, e.g., lme4:::coef.merMod(), which returns BLUPs
>>>> rather than fixed effects, internally in the cv package but *not* to
>>>> mask the lme4 version of the method for users of the cv package -- that
>>>> could wreak havoc with their work. Doing this substantially simplifies
>>>> some of the code in the cv package.
>>>>
>>>> My question: Is it legitimate to define a method in a package for
>>>> internal use without registering it?
>>>>
>>>> This approach appears to work fine, and R CMD check doesn't complain,
>>>> although Roxygen does complain that the method isn't "exported"
>>>> (actually, isn't registered).
>>>>
>>>> Any advice or relevant information would be appreciated.
>>>>
>>>> Thank you,
>>>>    John
>>>> --
>>>> John Fox, Professor Emeritus
>>>> McMaster University
>>>> Hamilton, Ontario, Canada
>>>> web: https://www.john-fox.ca/
>>>> --
>>>>
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