[Rd] S3 dispatch does not work for generics defined inside an environment

[Duncan Murdoch]

On 30/06/2021 6:51 a.m., Taras Zakharko wrote:
> @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?

Surely not.  That would set the result to 1 if the user had 
_R_S3_METHOD_LOOKUP_USE_TOPENV_AS_DEFENV_=FALSE.  The default for that 
env variable in the R code in src/library/utils/objects.R is explicitly 
TRUE, and it should surely be treated the same in C code.
> 
> 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. 

No, the StringFalse() call tries to determine if the string is set to 
something that looks like FALSE.  So it will be 1 if not set or set but 
not "FALSE" (or equivalent), which is the same thing as saying the 
default for that env var should be treated as TRUE.

Duncan Murdoch

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 using gmail.com> wrote:
>>
>> On Wed, Jun 30, 2021 at 5:17 AM Duncan Murdoch <murdoch.duncan using 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 using r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>>
>>
>> -- 
>> Joshua Ulrich  |  about.me/joshuaulrich
>> FOSS Trading  |  www.fosstrading.com
>