Can I remove an element in … (dot-dot-dot) and pass it on?

Question

Is it possible to remove an element from ... and pass ... onto other functions? My first two attempts failed:

parent = function(...)
{

   a = list(...)
            


        

Answer 1

Your child function is erroneous. Try

> child(a=1)
Error in str(a) : object 'a' not found

edit : no longer applicable.

The ... argument should only be used to pass parameters to a next function. You cannot get the parameters from there that easily, unless you convert them to a list. So your child function could be :

child <- function(...)
{
  mc <- match.call()  # or mc <- list(...)
  str(mc$a)
}

Which doesn't make sense. You can't know whether the user specified a or not. The correct way would be to include a as an argument in your function. the ... is to pass arguments to the next one :

child <- function(a, ...){
    str(a,...)
}

Then you could do :

parent <- function(...){

   mc <- match.call()
   mc$toRemove <- NULL
   mc[[1L]] <- as.name("child")
   eval(mc)

}

or use the list(...) and do.call() construct @Gavin proposed. The benefit of match.call() is that you can include non-dot arguments as well. This allows your parent function to specify defaults for the child :

parent <- function(a=3, ...){
    ... (see above)
}