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check_exclusive() checks that only one argument is supplied out of a set of mutually exclusive arguments. An informative error is thrown if multiple arguments are supplied.

Usage

check_exclusive(
  ...,
  .require = TRUE,
  .frame = caller_env(),
  .error_call = .frame
)

Arguments

...

Function arguments.

.require

Whether at least one argument must be supplied.

.frame

Environment where the arguments in ... are defined.

.error_call

The execution environment of a currently running function, e.g. caller_env(). The function will be mentioned in error messages as the source of the error. See the call argument of abort() for more information.

Value

The supplied argument name as a string. If .require is FALSE and no argument is supplied, the empty string "" is returned.

Examples

f <- function(x, y) {
  switch(
    check_exclusive(x, y),
    x = message("`x` was supplied."),
    y = message("`y` was supplied.")
  )
}

# Supplying zero or multiple arguments is forbidden
try(f())
#> Error in f() : 
#>   One of `x` or `y` must be supplied.
try(f(NULL, NULL))
#> Error in f(NULL, NULL) : 
#>   Exactly one of `x` or `y` must be supplied.

# The user must supply one of the mutually exclusive arguments
f(NULL)
#> `x` was supplied.
f(y = NULL)
#> `y` was supplied.


# With `.require` you can allow zero arguments
f <- function(x, y) {
  switch(
    check_exclusive(x, y, .require = FALSE),
    x = message("`x` was supplied."),
    y = message("`y` was supplied."),
    message("No arguments were supplied")
  )
}
f()
#> No arguments were supplied