R devel - Jun 2021 - S3 dispatch does not work for generics defined inside an environment

On Wed, Jun 30, 2021 at 5:17 AM Duncan Murdoch <murdoch.duncan at
gmail.com> wrote:
>
> On 30/06/2021 5:22 a.m., Taras Zakharko wrote:
> > Dear all,
> >
> > I have a generic function and a bunch of methods defined in a separate
environment. Here is a reduced example:
> >
> >     env <- local({
> >       # define the generic function and the method
> >       myfun <- function(x) UseMethod("myfun")
> >       myfun.myclass <- function(x) print("called
myfun.myclass?)
> >
> >       # register the method
> >       .S3method("myfun", "myclass", myfun.myclass)
> >
> >       environment()
> >    })
> >
> > Since the method has been registered, I hoped that invocation like
this would work:
> >
> >     env$myfun(structure(0, class = "myclass?))
> >
> > However, this results in a ?no applicable method" error.
> >
> > It is my understanding that registerS3method (called by .S3method)
will install the method string in the .__S3MethodsTable__. table of the
environment where the generic function is defined, and this table is
subsequently used by usemethod() inside R, so I am puzzled that the dispatch
does not work. I checked and the  .__S3MethodsTable__. of env is indeed setup
correctly. I also tried manually adding the method string to the global
.__S3MethodsTable__. inside .BaseNamespaceEnv to no effect.
> >
> > In fact, the only way to make it work is to define either myfun or 
myfun.myclas in the global environment, which is something I would like to
avoid.
> >
> > Thank you in advance for any pointers!
> >
>
> registerS3method has an additional parameter "envir" which I
believe
> would end up set to env in your code.  So this works:
>
>  > eval(expression(myfun(structure(0, class = "myclass"))),
envir = env)
> [1] "called myfun.myclass"
>
> You could probably also call registerS3method with envir specified
> appropriately and get your original expression to work.
>
That doesn't seem to work on 4.1.0 for me. The code below worked for
me in Oct-2020, though I'm not sure what version of R I was using at
the time. I was slow to upgrade to 4.0, so it was probably the latest
3.x version.

env <- new.env()
local({
   # define the generic function and the method
   myfun <- function(x) { UseMethod("myfun", x) }

   # register the method
   registerS3method("myfun", "myclass",
       function(x) { print("called myfun.myclass") },
       envir = env)
}, envir = env)
attach(env)
myfun(structure(0, class = "myclass"))

> Duncan Murdoch
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel


-- 
Joshua Ulrich  |  about.me/joshuaulrich
FOSS Trading  |  www.fosstrading.com

@Duncan: .S3method() calls registerS3method() with appropriate environmental
argument under the good, so that?s not the problem.

Anyway, I?ve been doing some debugging and I think I have found the issue. The
following snippet in src/objects.c
(https://github.com/wch/r-source/blob/ecc633b37d77fdd1cb27dda74d7f6b3684f0c01c/src/main/objects.c#L525)
sets the global lookup_use_topenv_as_defenv variable:


 if(lookup_use_topenv_as_defenv == -1) {
	lookup = getenv("_R_S3_METHOD_LOOKUP_USE_TOPENV_AS_DEFENV_");
	lookup_use_topenv_as_defenv = 
	    ((lookup != NULL) && StringFalse(lookup)) ? 0 : 1;
 }

Isn?t that supposed to be 

	lookup_use_topenv_as_defenv =  ((lookup != NULL) &&
StringFalse(lookup)) ? 1 : 0;

instead? 

The way the code works right now, methods will be looked up in top environment
exactly if _R_S3_METHOD_LOOKUP_USE_TOPENV_AS_DEFENV_ is not set. This seems
incompatible with what registerS3method() does (setting the .__S3MethodsTable__.
on the defining environment instead of the topenv). When I change 0 and 1
around, everything works as expected.

In the meantime, I can work around it by manually injecting __S3MethodsTable__
into .GlobalEnv (which is my topenv here).

I can open a bug report, but I would like to wait for some more comments. 

Best, 

Taras
> On 30 Jun 2021, at 12:39, Joshua Ulrich <josh.m.ulrich at gmail.com>
wrote:
> 
> On Wed, Jun 30, 2021 at 5:17 AM Duncan Murdoch <murdoch.duncan at
gmail.com> wrote:
>> 
>> On 30/06/2021 5:22 a.m., Taras Zakharko wrote:
>>> Dear all,
>>> 
>>> I have a generic function and a bunch of methods defined in a
separate environment. Here is a reduced example:
>>> 
>>>    env <- local({
>>>      # define the generic function and the method
>>>      myfun <- function(x) UseMethod("myfun")
>>>      myfun.myclass <- function(x) print("called
myfun.myclass?)
>>> 
>>>      # register the method
>>>      .S3method("myfun", "myclass",
myfun.myclass)
>>> 
>>>      environment()
>>>   })
>>> 
>>> Since the method has been registered, I hoped that invocation like
this would work:
>>> 
>>>    env$myfun(structure(0, class = "myclass?))
>>> 
>>> However, this results in a ?no applicable method" error.
>>> 
>>> It is my understanding that registerS3method (called by .S3method)
will install the method string in the .__S3MethodsTable__. table of the
environment where the generic function is defined, and this table is
subsequently used by usemethod() inside R, so I am puzzled that the dispatch
does not work. I checked and the  .__S3MethodsTable__. of env is indeed setup
correctly. I also tried manually adding the method string to the global
.__S3MethodsTable__. inside .BaseNamespaceEnv to no effect.
>>> 
>>> In fact, the only way to make it work is to define either myfun or 
myfun.myclas in the global environment, which is something I would like to
avoid.
>>> 
>>> Thank you in advance for any pointers!
>>> 
>> 
>> registerS3method has an additional parameter "envir" which I
believe
>> would end up set to env in your code.  So this works:
>> 
>>> eval(expression(myfun(structure(0, class = "myclass"))),
envir = env)
>> [1] "called myfun.myclass"
>> 
>> You could probably also call registerS3method with envir specified
>> appropriately and get your original expression to work.
>> 
> That doesn't seem to work on 4.1.0 for me. The code below worked for
> me in Oct-2020, though I'm not sure what version of R I was using at
> the time. I was slow to upgrade to 4.0, so it was probably the latest
> 3.x version.
> 
> env <- new.env()
> local({
>   # define the generic function and the method
>   myfun <- function(x) { UseMethod("myfun", x) }
> 
>   # register the method
>   registerS3method("myfun", "myclass",
>       function(x) { print("called myfun.myclass") },
>       envir = env)
> }, envir = env)
> attach(env)
> myfun(structure(0, class = "myclass"))
> 
> 
>> Duncan Murdoch
>> 
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
> 
> 
> 
> -- 
> Joshua Ulrich  |  about.me/joshuaulrich
> FOSS Trading  |  www.fosstrading.com