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utils::isS3stdGeneric chokes on primitives and identity

7 messages · Antoine Fabri, Kurt Hornik, Gabriel Becker

#
Dear R-devel,

utils::isS3stdGeneric tries to subset the body of the function it's fed,
primitives don't like that because they don't have a body, identity doesn't
like it either because it's body is a symbol.

According to the doc, any function is a legal input.

See below:

identity
#> function (x)
#> x
#> <bytecode: 0x0000000013d6da28>
#> <environment: namespace:base>

max
#> function (..., na.rm = FALSE)  .Primitive("max")

isS3stdGeneric(identity)
#> Error in bdexpr[[1L]]: objet de type 'symbol' non indi?able

isS3stdGeneric(max)
#> Error in while (as.character(bdexpr[[1L]]) == "{") bdexpr <-
bdexpr[[2L]]: l'argument est de longueur nulle

Here is a simple fix :

isS3stdGeneric <- function(f) {
  {
    bdexpr <- body(f)
    if(is.null(bdexpr) || !is.call(bdexpr)) return(FALSE)
    while (as.character(bdexpr[[1L]]) == "{") bdexpr <- bdexpr[[2L]]
    ret <- is.call(bdexpr) && identical(bdexpr[[1L]], as.name("UseMethod"))
    if (ret)
      names(ret) <- bdexpr[[2L]]
    ret
  }
}

isS3stdGeneric(identity)
#> [1] FALSE
isS3stdGeneric(max)
#> [1] FALSE

Best,

Antoine
#
I added that so I can look at the proposed fix and put it or something
similar in bugzilla for review final review.

Apologies for the oversight.

~G

On Wed, Aug 19, 2020 at 3:40 PM Antoine Fabri <antoine.fabri at gmail.com>
wrote:

  
  
#
Fixed now with

-    while(as.character(bdexpr[[1L]]) == "{")
+    while(is.call(bdexpr) && (as.character(bdexpr[[1L]]) == "{"))

(the suggested fix does not work on things like
foo <- function(x) {{ x }} 
...)

Best
-k

            

        
7 days later
#
Should it work on traced functions ?

As it is now it doesn't.

Best,

Antoine

Le jeu. 20 ao?t 2020 ? 09:58, Kurt Hornik <Kurt.Hornik at wu.ac.at> a ?crit :

  
  
#
Trace adds something to the body of the function, so it does make sense
that it doesn't. Whether traced functions still technically meet the
definition of standard s3 generic or not is, I suppose, up for debate, but
I would say that they should, I think.

As before, if desired I can work on a patch for this if desired, or someone
on R-core can just take care of it if that is easier.

Best,
~G

On Thu, Aug 27, 2020 at 11:22 AM Antoine Fabri <antoine.fabri at gmail.com>
wrote:

  
  
1 day later
#
Hi all,

I have a patch that fixes this and also fixes/improves debugcall so that it
supports pkg::fun(obj) and pkg:::fun(obj) style calls. I'm going to test it
a bit more and add a regression test for isS3stdGeneric and then I will
submit it to bugzilla tonight or tomorrow morning.

Best,
~G

On Thu, Aug 27, 2020 at 5:28 PM Gabriel Becker <gabembecker at gmail.com>
wrote:

  
  
#
Submitted to bugzilla here:
https://bugs.r-project.org/bugzilla/show_bug.cgi?id=17901

On Sat, Aug 29, 2020 at 1:57 PM Gabriel Becker <gabembecker at gmail.com>
wrote: