[R-pkg-devel] failing S3 dispatch

[Duncan Murdoch]

On 21/10/2021 1:23 p.m., Jens Oehlschlägel wrote:
> Thanks Duncan,
> 
> I finally found the reason for the mysterious dispatch-failure: I had an
> unwanted and unexported replicated definition of the 'clone' generic in
> ff's namespace (a left-over).
> 
> I still don't understand how this prevented the proper dispatch since
> the duplicate in ff's namespace it was *not* called. I further
> experimented and *any* non-exported object matching the name of the
> generic caused the problem. Scary, maybe worth a check!

Your NAMESPACE file contains

   S3method("clone",ff)

When R installs your package, it has to figure out where "clone" lives. 
  You imported a copy of it from bit, and then overwrote that imported 
copy with the replicated definition.

That created a new generic belonging to ff, and that's the one that your 
clone.ff method was attached to.

When you called clone(x), you called the bit::clone generic which never 
received the registration, so dispatch to clone.ff never happened.

It makes sense:  you don't want a generic in one package to interfere 
with an unrelated generic in another package that happens to have the 
same name.

Duncan Murdoch


> 
> Anyhow, removing the non-exported object solved the problem.
> 
> Best regards
> 
> Jens
> 
> 
> On 20.10.21 13:43, Jens Oehlschlägel wrote:
>> Thank you Duncan,
>>
>> bit NAMESPACE has
>>
>> S3method(clone,default)
>> export(clone)
>>
>> ff NAMESPACE has
>>
>> import(bit)
>> # wish of CRAN maintainers: export another time here (now maintained
>> and exported in bit)
>> # without this R CMD CHECK complained, but with it R CMD CHECK
>> complains also, how to export again and why?
>> # clone
>> #,clone.default
>>   clone.ff
>> ,clone.ffdf
>> S3method("clone",ff)
>> S3method(clone, ffdf)
>> # wish of CRAN maintainers: export another time here (now maintained
>> and exported in bit)
>> #S3method(clone, default)
>>
>> Best
>>
>> Jens
>>
>>
>>
>> On 20.10.21 11:02, Duncan Murdoch wrote:
>>> On 19/10/2021 3:43 p.m., Jens Oehlschlägel wrote:
>>>> I didn't find an answer elsewhere:
>>>>
>>>> My package 'bit' creates a S3 generic 'clone' and exports it.
>>>> Furthermore it registers a S3 method 'clone.default' (not exported).
>>>>
>>>> My package 'ff' imports package 'bit' and exports and registers a
>>>> new S3
>>>> method 'clone.ff'. However, calling 'clone(ffobj)' dispatches to
>>>> clone.default instead of clone.ff !? Why?
>>>
>>> You should show us the NAMESPACE entries involving clone and clone.ff
>>> from ff.
>>>
>>> Some comments that may or may not be relevant:
>>>
>>>   - Normally you wouldn't export clone.ff, it's enough to register it
>>> using S3method().
>>>
>>>   - You may have created a new generic named clone, and that's what
>>> clone.ff would attach itself to.  You can have bit::clone and
>>> ff::clone as different generics and that would cause problems.
>>>
>>>>
>>>> What is the recommended way to create new S3-methods that get
>>>> dispatched? In earlier versions of the packages I simply exported
>>>> everything - that worked.
>>>
>>> I import the generic and use S3method(generic, method).  I don't
>>> export the methods, so I wouldn't be able to call z <- clone.ff(a).
>>>
>>> Duncan Murdoch
>>>
>>>>
>>>> Best
>>>>
>>>>
>>>> Jens
>>>>
>>>>
>>>>    > require(ff)
>>>>    >
>>>>    > a <- as.ff(0:9)
>>>>    > class(x)
>>>> [1] "ff_vector" "ff"
>>>>    >
>>>>    > x <- clone(a)
>>>>    > y <- bit:::clone.default(a)
>>>>    > z <- clone.ff(a)
>>>>    >
>>>>    > # cloned ffobjects should have different filenames>
>>>>
>>>>    > filename(a)  # original
>>>> [1] "/tmp/Rtmpk17JRZ/ff/clone1ed54cbb5060.ff"
>>>>    >
>>>>    > filename(x)  # unexpected equal (dispatch to clone.default)
>>>> [1] "/tmp/Rtmpk17JRZ/ff/clone1ed54cbb5060.ff"
>>>>    >
>>>>    > filename(y)  # expected equal
>>>> [1] "/tmp/Rtmpk17JRZ/ff/clone1ed54cbb5060.ff"
>>>>    >
>>>>    > filename(z)  # OK
>>>> [1] "/tmp/Rtmpk17JRZ/ff/clone1ed551d3ee66.ff"
>>>>
>>>>    > version
>>>>                   _
>>>> platform       x86_64-pc-linux-gnu
>>>> arch           x86_64
>>>> os             linux-gnu
>>>> system         x86_64, linux-gnu
>>>> status
>>>> major          4
>>>> minor          1.1
>>>> year           2021
>>>> month          08
>>>> day            10
>>>> svn rev        80725
>>>> language       R
>>>> version.string R version 4.1.1 (2021-08-10)
>>>> nickname       Kick Things
>>>>
>>>> ______________________________________________
>>>> R-package-devel using r-project.org mailing list
>>>> https://stat.ethz.ch/mailman/listinfo/r-package-devel
>>>>
>>>
>>
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