Dear Wolfgang,
I think this new behaviour is related to the following R 4.0.0 NEWS item:
> S3 method lookup now by default skips the elements of the search path between
> the global and base environments.
Your environment "myenv" is attached at position 2 of the search() path
and thus now skipped in S3 method lookup.
I have just noticed that
attr(methods(class="myclass"), "info")
getS3method("print", "myclass")
both still find your function in myenv although the generic's
UseMethod() won't. I find this a bit confusing.
A solution to make R >= 4.0.0 find your method is to register the S3
method using the new function .S3method (intended for R scripts, not
packages). After running
.S3method("print", "myclass", myenv$print.myclass)
your method will be found from the generic.
Best regards,
Sebastian
Am 12.05.20 um 20:05 schrieb Viechtbauer, Wolfgang (SP):
> Dear All,
>
> In R 3.6.3 (and earlier), method dispatch used to work for methods stored in
> local environments that are attached to the search path. For example:
>
> myfun <- function(y) {
> out <- list(y=y)
> class(out) <- "myclass"
> return(out)
> }
>
> print.myclass <- function(x, ...) print(formatC(x$y, format="f", digits=5))
>
> myfun(1:4)
>
> # prints: [1] "1.00000" "2.00000" "3.00000" "4.00000"
>
> rm(print.myclass)
> myenv <- new.env()
> myenv$print.myclass <- local(function(x, ...) print(formatC(x$y, format="f",
> digits=5)), myenv)
> attach(myenv)
> myfun(1:4)
>
> # still prints: [1] "1.00000" "2.00000" "3.00000" "4.00000"
>
> But since R 4.0.0, this no longer words and the above prints:
>
> $y
> [1] 1 2 3 4
>
> attr(,"class")
> [1] "myclass"
>
> Is this intended? And is there a way to still make this work?
>
> Best,
> Wolfgang
>
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