Method to call downstream function with appropriate ... args?

[jmw86069]

Due respect, I'm not sure if this is the best place to ask the question.

Scenario:

• Parent function passes ... to one or more downstream functions.
• Downstream function does not allow ..., and has a lot of arguments (83).
• Parent function would like to allow ... for customization of downstream function.
• Parent function would like to pass only appropriate ... arguments to downstream function, to avoid causing an error.

From section 6.2.4 https://adv-r.hadley.nz/functions.html#function-fundamentals it appears that do.call(function, args) could be used for this purpose. I wonder if some type of function would live in this package?

Example scenario:

my_lil_function <- function(x, ...) {
   mean_function(x, ...)
}
mean_function <- function(x, na.rm=FALSE) {
   mean(x, na.rm=na.rm)
}
# success
my_lil_function(c(1, 2.5, 3, NA), na.rm=TRUE)
# error
my_lil_function(c(1, 2.5, 3, NA), na.rm=TRUE, color="red")
# Error in mean_function(x, ...) : unused argument (color = "red")

Rough idea of workaround:

# new function for this package?
call_fn_ellipsis <- function(FUN, ...) {
   FUN_argnames <- names(formals(FUN));
   if ("..." %in% FUN_argnames) {
      # if FUN allows ... then pass all of ...
      FUN(...)
   } else {
      # if FUN does not allow ... then pass only what it accepts
      arglist <- list(...)
      argkeep <- which(names(arglist) %in% FUN_argnames)
      arguse <- arglist[argkeep]
      do.call(FUN, arguse)
   }
}

# new method would involve using do.call()
my_new_lil_function <- function(x, ...) {
   args_to_send <- c(list(x=x),
      list(...));
   do.call(call_fn_ellipsis,
      c(FUN=mean_function, args_to_send))
}
# now success
my_new_lil_function(c(1, 2.5, 3, NA), na.rm=TRUE, color="red")
# [1] 2.17

Main drivers:

• I don't want to add 83 arguments to my_lil_function() in order to avoid using ...
• I want to use ... for customizations to two different functions called by my_lil_function()
• I do not control the downstream function, so I can't add ... to that function's arguments.

Suggestions, feedback, guidance welcomed!
Maybe there is an R package function that already performs this step.
Thank you!

[jmw86069]

For what it's worth, there is a simpler way to call call_fn_ellipsis() above.

my_new_lil_function2 <- function(x, ...) {
   call_fn_ellipsis(FUN=mean_function, x=x, ...)
}
my_new_lil_function2(c(1, 2.5, 3, NA), na.rm=TRUE, color="red")
# 2.17