`on.exit()` example does not include `add = TRUE` when changing multiple options inside a package function

[tylermorganwall]

In this example in the Code Issues section, add = TRUE is not specified when setting multiple on.exit() calls. This will lead to a the first two on.exit code snippets not being executed and thus failing to reset to the pre-specified par/option settings at the end of the function.

foo <- function(x){
  
  # par():
  oldpar <- par(mfrow = c(2,2))
  on.exit(par(oldpar))
  
  # options():
  oldop <- options(digits = 3)
  on.exit(options(oldop))
  
  # setwd():
  oldwd <- setwd(".")
  on.exit(setwd(oldwd))
  
  # your code which requires a changed option
  
}

This should be changed to the following:

foo <- function(x){
  
  # par():
  oldpar <- par(mfrow = c(2,2))
  on.exit(par(oldpar))
  
  # options():
  oldop <- options(digits = 3)
  on.exit(options(oldop), add = TRUE)
  
  # setwd():
  oldwd <- setwd(".")
  on.exit(setwd(oldwd), add = TRUE)
  
  # your code which requires a changed option
  
}

[Baltmann01]

Thanks for spotting that! I change the example code to

foo <- function(x){

  
 # par():
  old <- par(mfrow = c(2,2))
  on.exit(par(old))
 
 # your code which requires a changed option  
}

to avoid confusion and added a textbox warning at the end of the recipe stating that one needs to set add = TRUE if more than one option is changed.