On Wed, Jun 30, 2021 at 5:17 AM Duncan Murdoch <murdoch.dun...@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
>
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> https://stat.ethz.ch/mailman/listinfo/r-devel
--
Joshua Ulrich | about.me/joshuaulrich
FOSS Trading | www.fosstrading.com
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