[Rd] S3 method dispatch for methods in local environments

[Martin Maechler]

>>>>> Viechtbauer, Wolfgang (SP) 
>>>>>     on Tue, 12 May 2020 18:05:32 +0000 writes:

    > 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? 

yes, most probably, unless

    > And is there a way to still make this work?

Using  the new

       .S3method(<generic>, <class>, <method_function>)

had been intended as substitute.  Can you try it with your
attached-environment (which makes sense!)  approach ?

Best,
Martin