Tools for Working with ...

In S3 generics, it's useful to take ... so that methods can have additional argument. But this flexibility comes at a cost: misspelled arguments will be silently ignored. The ellipsis packages is an experiment that allows a generic to warn if any arguments passed in ... are not used.

Adding ... to an S3 generic allows methods to take additional arguments, but it comes with a big downside: any misspelled or extraneous arguments will be silently ignored. This package explores an approach to making ... safer, by supply a function that a generic can use to warn if any elements of ... were not evaluated.

In the long run, this code is likely to live elsewhere (maybe R-core might be interested in making it part of base R). This repository tracks the current state of the experiment.

Thanks to Jenny Bryan for the idea, and Lionel Henry for the heart of the implementation.

Installation

devtools::install_github("hadley/ellipsis")

Example

safe_median() works like median() but warns if any elements of ... are never evaluated

library(ellipsis)
x <- c(1:10, NA)
 
safe_median(x)
#> [1] 5.5
safe_median(x, TRUE)
#> Warning: Some components of ... were not used: ..1
#> [1] 5.5
safe_median(x, na.rm = TRUE)
#> [1] 5.5
safe_median(x, na.mr = TRUE)
#> Warning: Some components of ... were not used: na.mr
#> [1] 5.5