[Rd] S3 dispatch for S4 subclasses only works if variable "extends" is accessible from global environment

[Hadley Wickham]

This might be too big a change - but is it worth reconsidering the
behaviour of Rscript? Maybe the simplest fix would be simply to always
load the methods package.  (I think historically it didn't because
loading methods took a long time, but that is no longer true)

Hadley

On Tue, Apr 19, 2016 at 10:37 AM, Gabriel Becker <gmbecker at ucdavis.edu> wrote:
> Does it make sense to be able to load an S4 object without the methods
> package being attached? I'm not sure implementation-wise how easy this
> would be, but it seems like any time there is an S4 object around, the
> methods package should be available to deal with it.
>
> ~G
>
> On Tue, Apr 19, 2016 at 7:34 AM, Michael Lawrence <lawrence.michael at gene.com
>> wrote:
>
>> Right, R_has_methods_attached() uses that. Probably not the right
>> check, since it refers to S4 dispatch, while S4_extends() is used by
>> S3 dispatch.
>>
>> Perhaps S4_extends() should force load the methods package? The above
>> example works after fixing the check to ensure that R_MethodsNamespace
>> is not R_GlobalEnv, but one could load a serialized S4 object and
>> expect S3 dispatch to work with Rscript.
>>
>> On Tue, Apr 19, 2016 at 6:51 AM, Gabriel Becker <gmbecker at ucdavis.edu>
>> wrote:
>> > See also .isMethodsDispatchOn, which is what trace uses to decide if the
>> > methods package needs to be loaded.
>> >
>> > ~G
>> >
>> > On Tue, Apr 19, 2016 at 5:34 AM, Michael Lawrence
>> > <lawrence.michael at gene.com> wrote:
>> >>
>> >> Not sure why R_has_methods_attached() exists. Maybe Martin could shed
>> >> some light on that.
>> >>
>> >> On Mon, Apr 18, 2016 at 11:50 PM, Kirill Müller
>> >> <kirill.mueller at ivt.baug.ethz.ch> wrote:
>> >> > Thanks for looking into it, your approach sounds good to me. See also
>> >> > R_has_methods_attached()
>> >> >
>> >> > (
>> https://github.com/wch/r-source/blob/42ecf5f492a005f5398cbb4c9becd4aa5af9d05c/src/main/objects.c#L258-L265
>> ).
>> >> >
>> >> > I'm fine with Rscript not loading "methods", as long as everything
>> works
>> >> > properly with "methods" loaded but not attached.
>> >> >
>> >> >
>> >> > -Kirill
>> >> >
>> >> >
>> >> >
>> >> > On 19.04.2016 04:10, Michael Lawrence wrote:
>> >> >>
>> >> >> Right, the methods package is not attached by default when running R
>> >> >> with Rscript. We should probably remove that special case, as it
>> >> >> mostly just leads to confusion, but that won't happen immediately.
>> >> >>
>> >> >> For now, the S4_extends() should probably throw an error when the
>> >> >> methods namespace is not loaded. And the check should be changed to
>> >> >> directly check whether R_MethodsNamespace has been set to something
>> >> >> other than the default (R_GlobalEnv). Agreed?
>> >> >>
>> >> >> On Mon, Apr 18, 2016 at 4:35 PM, Kirill Müller
>> >> >> <kirill.mueller at ivt.baug.ethz.ch> wrote:
>> >> >>>
>> >> >>> Scenario: An S3 method is declared for an S4 base class but called
>> for
>> >> >>> an
>> >> >>> instance of a derived class.
>> >> >>>
>> >> >>> Steps to reproduce:
>> >> >>>
>> >> >>>> Rscript -e "test <- function(x) UseMethod('test', x); test.Matrix
>> <-
>> >> >>>> function(x) 'Hi'; MatrixDispatchTest::test(Matrix::Matrix())"
>> >> >>>
>> >> >>> Error in UseMethod("test", x) :
>> >> >>>    no applicable method for 'test' applied to an object of class
>> >> >>> "lsyMatrix"
>> >> >>> Calls: <Anonymous>
>> >> >>> 1: MatrixDispatchTest::test(Matrix::Matrix())
>> >> >>>
>> >> >>>> Rscript -e "extends <- 42; test <- function(x) UseMethod('test',
>> x);
>> >> >>>> test.Matrix <- function(x) 'Hi';
>> >> >>>> MatrixDispatchTest::test(Matrix::Matrix())"
>> >> >>>
>> >> >>> [1] "Hi"
>> >> >>>
>> >> >>> To me, it looks like a sanity check in line 655 of src/main/attrib.c
>> >> >>> is
>> >> >>> making wrong assumptions, but there might be other reasons.
>> >> >>>
>> >> >>>
>> >> >>> (
>> https://github.com/wch/r-source/blob/780021752eb83a71e2198019acf069ba8741103b/src/main/attrib.c#L655-L656
>> )
>> >> >>>
>> >> >>> Same behavior in R 3.2.4, R 3.2.5 and R-devel r70420.
>> >> >>>
>> >> >>>
>> >> >>> Best regards
>> >> >>>
>> >> >>> Kirill
>> >> >>>
>> >> >>> ______________________________________________
>> >> >>> R-devel at r-project.org mailing list
>> >> >>> https://stat.ethz.ch/mailman/listinfo/r-devel
>> >> >>>
>> >> >
>> >> >
>> >>
>> >> ______________________________________________
>> >> R-devel at r-project.org mailing list
>> >> https://stat.ethz.ch/mailman/listinfo/r-devel
>> >
>> >
>> >
>> >
>> > --
>> > Gabriel Becker, PhD
>> > Associate Scientist (Bioinformatics)
>> > Genentech Research
>>
>
>
>
> --
> Gabriel Becker, PhD
> Associate Scientist (Bioinformatics)
> Genentech Research
>
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>
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> https://stat.ethz.ch/mailman/listinfo/r-devel



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