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

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!

Best, 

Taras

P.S. If you are wondering what I am trying to achieve here ? we have a very
large codebase and I am trying to use environments as a type of ?poor man?s
namespaces? to organize code in a modular fashion. But of course it?s all
pointless if I can?t get the generics to work reliably.

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.

Duncan Murdoch

Taras,
> P.S. If you are wondering what I am trying to achieve here ? we have a
> very large codebase and I am trying to use environments as a type of
> ?poor man?s namespaces? to organize code in a modular fashion. But of
> course it?s all pointless if I can?t get the generics to work
> reliably.
i'm not knowledgeable about S3.  but, a different way to try to
modularize large code bases is to split them into separate packages.
just in case you hadn't already thought about, and rejected, that idea.

cheers, Greg