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

[Taras Zakharko]

I had another glance at the code and now I’m convinced that this is the bug in registerS3method(). Default R behavior (in objects.c) appears to be to look for method definitions in the top environment, not the defining environment, but registerS3method() registers the method in the defining environment. I think registerS3method() should be changed to something like:


- if (typeof(genfun) == "closure”) 
-            environment(genfun)
------------
+ if (typeof(genfun) == "closure”) 
+ if(isFALSE(Sys.getenv("_R_S3_METHOD_LOOKUP_USE_TOPENV_AS_DEFENV_”))  environment(genfun) else topenv(environment(genfun)) 

in order to match the behavior of do_usemethod()

Best, 

Taras


> On 30 Jun 2021, at 12:51, Taras Zakharko <taras.zakharko using uzh.ch> 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? 
> 
> 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 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
>