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withr - run code ‘with’ modified state

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A set of functions to run code with safely and temporarily modified global state. There are two sets of functions, those prefixed with with_ and those with local_. The former reset their state as soon as the code argument has been evaluated. The latter reset when they reach the end of their scope, usually at the end of a function body.

Many of these functions were originally a part of the devtools package, this provides a simple package with limited dependencies to provide access to these functions.

  • with_collate() / local_collate() - collation order
  • with_dir() / local_dir() - working directory
  • with_envvar() / local_envvar() - environment variables
  • with_libpaths() / local_libpaths() - library paths
  • with_locale() / local_locale() - any locale setting
  • with_makevars() / local_makevars() - Makevars variables
  • with_options() / local_options() - options
  • with_par() / local_par() - graphics parameters
  • with_path() / local_path() - PATH environment variable
  • with_*() and local_() functions for the built in R devices, bmp, cairo_pdf, cairo_ps, pdf, postscript, svg, tiff, xfig, png, jpeg.
  • with_connection() / local_connection() - R connections.
  • with_package(), with_namespace() and with_environment() - to run code with modified object search paths.
  • with_tempfile() / local_tempfile() - Create and clean up a temp file.
  • with_file() / local_file() - Create and clean up a normal file.

There are also with_() and local_() functions to construct new with_* and local_* functions if needed.

Sys.getenv("WITHR")
#> [1] ""
with_envvar(c("WITHR" = 2), Sys.getenv("WITHR"))
#> [1] "2"
Sys.getenv("WITHR")
#> [1] ""

with_envvar(c("A" = 1),
  with_envvar(c("A" = 2), action = "suffix", Sys.getenv("A"))
)
#> [1] "1 2"

local functions

These functions are variants of the corresponding with_() function, but rather than resetting the value at the end of the function call they reset when the current context goes out of scope. This is most useful for using within functions.

f <- function(x) {
  local_envvar(c("WITHR" = 2))
  Sys.getenv("WITHR")
}
Sys.getenv("WITHR")
#> [1] ""

See Also