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.ulr...@gmail.com> wrote:
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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