Facilitates Results Caching in R Packages Using the Pins Package • pkgpins

pkgpins builds upon the pins package and strives to provide R package authors a simple and standardized way to cache results on the filesystem in a suitable user directory.

How it works

TODO: describe design (separate user-cache pins board per pkg and pkg version etc.)

Predefined parameter labels

There are two predefined parameter labels available in pkgsnip which fit typical use cases of this package. They are intended to be used in @param roxygen2 tags ¹ as follows:

#' @param max_cache_age `r pkgsnip::param_lbl("max_cache_age")`
#' @param use_cache `r pkgsnip::param_lbl("use_cache")`

The above inline R code will eventually result in this:

#' @param max_cache_age Duration after which cached results are refreshed (i.e. newly fetched). A valid [lubridate duration][lubridate::as.duration]. Use `Inf` to disable cache expiry. Only relevant if `use_cache = TRUE`.
#' @param use_cache Whether or not to return cached results if possible. If `FALSE`, results are always newly fetched regardless of `max_cache_age`.

Installation

To install the latest development version of pkgpins, run the following in R:

if (!("remotes" %in% rownames(installed.packages()))) {
  install.packages(pkgs = "remotes",
                   repos = "https://cloud.r-project.org/")
}

remotes::install_gitlab(repo = "rpkg.dev/pkgpins")

Usage

The (function) reference is found here.

Development

R Markdown format

This package’s source code is written in the R Markdown file format to facilitate practices commonly referred to as literate programming. It allows the actual code to be freely mixed with explanatory and supplementary information in expressive Markdown format instead of having to rely on # comments only.

All the .gen.R suffixed R source code found under R/ is generated from the respective R Markdown counterparts under Rmd/ using pkgpurl::purl_rmd()². Always make changes only to the .Rmd files – never the .R files – and then run pkgpurl::purl_rmd() to regenerate the R source files.

Coding style

This package borrows a lot of the Tidyverse design philosophies. The R code adheres to the principles specified in the Tidyverse Design Guide wherever possible and is formatted according to the Tidyverse Style Guide (TSG) with the following exceptions:

Line width is limited to 160 characters, double the limit proposed by the TSG (80 characters is ridiculously little given today’s high-resolution wide screen monitors).

Furthermore, the preferred style for breaking long lines differs. Instead of wrapping directly after an expression’s opening bracket as suggested by the TSG, we prefer two fewer line breaks and indent subsequent lines within the expression by its opening bracket:
```
# TSG proposes this
do_something_very_complicated(
  something = "that",
  requires = many,
  arguments = "some of which may be long"
)

# we prefer this
do_something_very_complicated(something = "that",
                              requires = many,
                              arguments = "some of which may be long")
```
This results in less vertical and more horizontal spread of the code and better readability in pipes.
Usage of magrittr’s compound assignment pipe-operator %<>% is desirable³.
Usage of R’s right-hand assignment operator -> is not allowed⁴.
R source code is not split over several files as suggested by the TSG but instead is (as far as possible) kept in the single file Rmd/pkgpins.Rmd which is well-structured thanks to its Markdown support.

As far as possible, these deviations from the TSG plus some additional restrictions are formally specified in the lintr configuration file .lintr, so lintr can be used right away to check for formatting issues:

pkgpurl::lint_rmd()

pkgpins