ijlyttle/withr

Methods For Temporarily Modifying Global State

withr - run code ‘with’ modified state

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.

• set_makevars()
• defer()
• defer_parent()
• with_collate() / local_collate() - collation order
• with_connection() / local_connection() - R connections.
• with_db_connection() / local_db_connection()
• with_dir() / local_dir() - working directory
• with_environment() / local_environment()
• 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_message_sink() / local_message_sink()
• with_options() / local_options() - options
• with_output_sink() / local_output_sink()
• with_par() / local_par() - graphics parameters
• with_path() / local_path() - PATH environment variable
• with_preserve_seed()
• with_rng_version() / local_rng_version()
• with_seed()
• with_temp_libpaths() / local_temp_libpaths()
• with_timezone() / local_timezone()
• with_*() and local_*() functions for the built in R devices, bmp, cairo_pdf, cairo_ps, pdf, postscript, svg, tiff, xfig, png, jpeg.
• with_package() / local_package(), with_namespace() / local_namespace() and with_environment() / local_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 instead of resetting the value at the end of the function call they reset when the current context goes out of scope. This is most useful within a function.

f <- function(x) {
  local_envvar(c("WITHR" = 2))
  Sys.getenv("WITHR")
}

f()
#> [1] "2"
Sys.getenv("WITHR")
#> [1] ""

See Also

• Devtools