[Rd] utils::isS3stdGeneric chokes on primitives and identity

[Gabriel Becker]

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 using gmail.com>
wrote:

> 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 indiçable
>
> 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
>
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>
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