Execute code in temporarily altered environment

All functions prefixed by with_ work as follows. First, a particular aspect of the global environment is modified (see below for a list). Then, custom code (passed via the code argument) is executed. Upon completion or error, the global environment is restored to the previous state. Each with_ function has a local_ variant, which instead resets the state when the current evaluation context ends (such as the end of a function).

Arguments pattern

`new`	`[various]`	Values for setting
`code`	`[any]`	Code to execute in the temporary environment
`...`		Further arguments

Usage pattern

with_...(new, code, ...)

withr functions

with_collate(): collation order
with_dir(): working directory
with_envvar(): environment variables
with_libpaths(): library paths, replacing current libpaths
with_locale(): any locale setting
with_makevars(): Makevars variables
with_options(): options
with_par(): graphics parameters
with_path(): PATH environment variable
with_sink(): output redirection

Creating new "with" functions

All with_ functions are created by a helper function, with_(). This functions accepts two arguments: a setter function and an optional resetter function. The setter function is expected to change the global state and return an "undo instruction". This undo instruction is then passed to the resetter function, which changes back the global state. In many cases, the setter function can be used naturally as resetter.

Author

Maintainer: Lionel Henry lionel@posit.co

Authors:

Jim Hester
Kirill Müller krlmlr+r@mailbox.org
Kevin Ushey kevinushey@gmail.com
Hadley Wickham hadley@posit.co
Winston Chang

Other contributors:

Jennifer Bryan [contributor]
Richard Cotton [contributor]
Posit Software, PBC [copyright holder, funder]

Examples

getwd()
#> [1] "/home/runner/work/withr/withr/docs/reference"
with_dir(tempdir(), getwd())
#> [1] "/tmp/RtmpcHnEKr"
getwd()
#> [1] "/home/runner/work/withr/withr/docs/reference"

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 variants are best used within other functions
f <- function(x) {
  local_envvar(c("WITHR" = 2))
  Sys.getenv("WITHR")
}
Sys.getenv("WITHR")
#> [1] ""