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Wrap a function to be called only once

Source: R/onetime.R
onetime_only.Rd

This takes a function and returns the same function wrapped by onetime_do(). Use it for code which should run only once, but which may be called from multiple locations. This frees you from having to use the same id multiple times.

Usage

onetime_only(
  .f,
  id = deprecate_calling_package(),
  path = default_lockfile_dir(),
  default = NULL,
  without_permission = "warn"
)

Arguments

.f

A function

id

Unique ID string. If this is unset, the name of the calling package will be used. Since onetime 0.2.0, not setting id is deprecated.

path

Directory to store lockfiles. The default uses a unique directory corresponding to the calling package, beneath rappdirs::user_config_dir(). Normally you should leave this as the default.

default

Value to return from .f if function was not executed.

without_permission

Character string. What to do if the user hasn't given permission to store files? "warn" runs the action with an extra warning; "run" runs the action with no warning; "pass" does nothing and returns the default; "stop" throws an error; "ask" asks for permission using check_ok_to_store(), and returns the default if it is not granted.

Value

A wrapped function. The function itself returns the result of .f, or default if the inner function was not called.

See also

onetime_do()

Examples

oo <- options(onetime.dir = tempdir(check = TRUE))
id <- sample(10000L, 1)

sample_once <- onetime_only(sample, id = id)
sample_once(1:10)
#>  [1] 10  6  7  2  4  3  8  5  1  9
sample_once(1:10)
#> NULL

onetime_reset(id)
options(oo)