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