globalsByName("..2") does not find argument '..2'

[HenrikBengtsson]

Issue

Consider:

> f <- function(...) { ..2 }
> f(a = 1, b = 2)
[1] 2

If we attempt to get ..2 using globalsByName(), it does not find that argument;

> f <- function(...) { globals::globalsByName("..2") }

> f(a = 1, b = 2)
$..2
[1] NA
attr(,"class")
[1] "DotDotDotList" "logical"      

attr(,"where")
attr(,"where")$..2
NULL

attr(,"class")
[1] "Globals" "list"   

Troubleshooting

The reason is that the code assumes exists("..2") is TRUE, but that's not the case, e.g.

> f <- function(...) { exists("..2") }
> f(a = 1, b = 2)
[1] FALSE

Solution

The solution is to work with .... Gist:

> f <- function(...) { 
  globals <- globals::globalsByName("...")
  if (is.list(globals[["..."]])) {
    if (length(globals[["..."]]) < 2) stop("the ... list contains fewer than 2 elements")
    args<- globals[["..."]]
    args <- args[2L]
    class(args) <- class(globals[["..."]])
    globals[["..."]] <- args
    globals
  }
}
> f(a = 1, b = 2)
$...
$b
[1] 2

attr(,"class")
[1] "DotDotDotList" "list"         

attr(,"where")
attr(,"where")$...
<environment: R_EmptyEnv>

attr(,"class")
[1] "Globals" "list"   

[HenrikBengtsson]

Implemented;

> f <- function(...) { globals::globalsByName("..2") }
g <- f(a = 1, b = 2, c = 3)
str(g)
List of 1
 $ ..2:List of 1
  ..$ : num 2
  ..- attr(*, "class")= chr [1:2] "DotDotDotList" "list"
 - attr(*, "where")=List of 1
  ..$ ..2:<environment: 0x557dae0e3d50> 
 - attr(*, "class")= chr [1:2] "Globals" "list"