arg_is: Check Argument Class

In arg: Clean and Simple Argument Checking

Check Argument Class

Description

Checks whether an argument is a of a specified class (arg_is()) or is not of a specified class (arg_is_not()).

Usage

arg_is(x, class, .arg = rlang::caller_arg(x), .msg = NULL, .call)

arg_is_not(x, class, .arg = rlang::caller_arg(x), .msg = NULL, .call)

Arguments

x	the argument to be checked
class	a character vector of one or more classes to check x against.
.arg	the name of the argument supplied to x to appear in error messages. The default is to extract the argument's name using rlang::caller_arg(). Ignored if .msg is supplied.
.msg	an optional alternative message to display if an error is thrown instead of the default message.
.call	the execution environment of a currently running function, e.g. .call = rlang::current_env(). The corresponding function call is retrieved and mentioned in error messages as the source of the error. Passed to err(). Set to NULL to omit call information. The default is to search along the call stack for the first user-facing function in another package, if any.

Details

arg_is() and arg_is_not() use inherits() to test for class membership. arg_is() throws an error only if no elements of class(x) are in class. arg_is_not() throws an error if any elements of class(x) are in class.

Sometimes this can be too permissive; combining arg_is() with arg_and() can be useful for requiring that an object is of multiple classes. Alternatively, combining arg_is_not() with arg_or() can be useful for requiring that an object is not a specific combination of classes. See Examples.

Value

Returns NULL invisibly if an error is not thrown.

See Also

inherits(), arg_or(); arg_data() for testing for specific kinds of objects (vectors, matrices, data frames, and lists)

Examples

obj <- structure(list(1),
                 class = "test")

try(arg_is(obj, "test"))            # No error
try(arg_is(obj, c("test", "quiz"))) # No error
try(arg_is(obj, "quiz"))            # Error

try(arg_is_not(obj, "test"))            # Error
try(arg_is_not(obj, c("test", "quiz"))) # Error
try(arg_is_not(obj, "quiz"))            # No error

# Multiple classes
obj2 <- structure(list(1),
                  class = c("test", "essay"))

try(arg_is(obj2, c("test", "quiz")))     # No error
try(arg_is_not(obj2, c("test", "quiz"))) # Error

## Require argument to be of multiple classes
try(arg_and(obj2,
            arg_is("test"),
            arg_is("quiz")))

## Require argument to not be a specific combination of
## multiple classes
try(arg_or(obj2,
           arg_is_not("test"),
           arg_is_not("essay")))

arg documentation built on April 9, 2026, 5:09 p.m.