Dispatch on a missing argument

Use class_missing to dispatch when no argument value is available. Omitted arguments with defaults dispatch on the default's class. Missing values detected by is.na() do not trigger class_missing dispatch.

Usage

class_missing

Value

Sentinel objects used for special types of dispatch.

Examples

foo := new_generic("x")
method(foo, class_numeric) <- function(x) "number"
method(foo, class_missing) <- function(x) "missing"
method(foo, class_any) <- function(x) "fallback"

foo(1)
#> [1] "number"
foo()
#> [1] "missing"
foo("")
#> [1] "fallback"