https://github.com/r-lib/ellipsis

Tools for Working with ...
https://github.com/r-lib/ellipsis

dot-dot-dot ellipsis r

Last synced: 1 day ago
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Tools for Working with ...

• Host: GitHub
• URL: https://github.com/r-lib/ellipsis
• Owner: r-lib
• License: other
• Created: 2018-07-06T20:49:16.000Z (over 6 years ago)
• Default Branch: main
• Last Pushed: 2021-10-27T22:49:18.000Z (about 3 years ago)
• Last Synced: 2024-11-23T23:58:43.285Z (18 days ago)
• Topics: dot-dot-dot, ellipsis, r
• Language: R
• Homepage: https://ellipsis.r-lib.org
• Size: 178 KB
• Stars: 141
• Watchers: 8
• Forks: 14
• Open Issues: 7
• Metadata Files:
  • Readme: README.Rmd
  • License: LICENSE

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• jimsghstars - r-lib/ellipsis - Tools for Working with ... (R)

README

        
---

output: github_document

---

```{r setup, include = FALSE}

knitr::opts_chunk$set(

  collapse = TRUE,

  comment = "#>",

  fig.path = "man/figures/README-",

  out.width = "100%"

)

```

# ellipsis

[![Lifecycle: maturing](https://img.shields.io/badge/lifecycle-maturing-blue.svg)](https://lifecycle.r-lib.org/articles/stages.html)

[![R-CMD-check](https://github.com/r-lib/ellipsis/workflows/R-CMD-check/badge.svg)](https://github.com/r-lib/ellipsis/actions)

[![CRAN status](https://www.r-pkg.org/badges/version/ellipsis)](https://cran.r-project.org/package=ellipsis)

[![Codecov test coverage](https://codecov.io/gh/r-lib/ellipsis/branch/master/graph/badge.svg)](https://codecov.io/gh/r-lib/ellipsis?branch=master)

Adding `...` to a function is a powerful technique because it allows you to accept any number of additional arguments. Unfortunately it comes with a big downside: any misspelled or extraneous arguments will be silently ignored. This package provides tools for making `...` safer:

* `check_dots_evaluated()` errors if any components of `...` are not evaluated.

  This allows an S3 generic to state that it expects every input to be 

  evaluated.

* `check_dots_unnamed()` errors if any components of `...` are named. This

  allows you to collect arbitrary unnamed arguments, warning if the user

  misspells a named argument.

* `check_dots_empty()` errors if `...` is used. This allows you to use `...` to

  force the user to supply full argument names, while still warning if an

  argument name is misspelled.

Thanks to [Jenny Bryan](https://github.com/jennybc) for the idea, and [Lionel Henry](https://github.com/lionel-) for the heart of the implementation.

## Installation

Install the released version from CRAN:

```{r, eval = FALSE}

install.packages("ellipsis")

```

Or the development version from GitHub:

```{r, eval = FALSE}

devtools::install_github("r-lib/ellipsis")

```

## Example

`mean()` is a little dangerous because you might expect it to work like `sum()`:

```{r}

sum(1, 2, 3, 4)

mean(1, 2, 3, 4)

```

This silently returns the incorrect result because `mean()` has arguments `x` and `...`. The `...` silently swallows up the additional arguments. We can use `ellipsis::check_dots_used()` to check that every input to `...` is actually used:

```{r, error = TRUE}

safe_mean <- function(x, ..., trim = 0, na.rm = FALSE) {

  ellipsis::check_dots_used()

  mean(x, ..., trim = trim, na.rm = na.rm)

}

safe_mean(1, 2, 3, 4)

```