Find a method for an S7 generic

method() takes a generic and class signature and performs method dispatch to find the corresponding method implementation. This is rarely needed because you'll usually rely on the the generic to do dispatch for you (via S7_dispatch()). However, this introspection is useful if you want to see the implementation of a specific method.

Usage

method(generic, class = NULL, object = NULL)

Arguments

generic

A generic function, i.e. an S7 generic, an external generic, an S3 generic, or an S4 generic.

class, object

Perform introspection either with a class (processed with as_class()) or a concrete object. If generic uses multiple dispatch then both object and class must be a list of classes/objects.

Value

Either a function with class S7_method or an error if no matching method is found.

See also

method_explain() to explain why a specific method was picked.

Examples

# Create a generic and register some methods
bizarro <- new_generic("bizarro", "x")
method(bizarro, class_numeric) <- function(x) rev(x)
method(bizarro, class_factor) <- function(x) {
  levels(x) <- rev(levels(x))
  x
}

# Printing the generic shows the registered method
bizarro
#> <S7_generic> bizarro(x, ...) with 3 methods:
#> 1: method(bizarro, class_integer)
#> 2: method(bizarro, class_double)
#> 3: method(bizarro, new_S3_class("factor"))

# And you can use method() to inspect specific implementations
method(bizarro, class = class_integer)
#> <S7_method> method(bizarro, class_integer)
#> function (x) 
#> rev(x)
#> <environment: 0x55e4936de390>
method(bizarro, object = 1)
#> <S7_method> method(bizarro, class_double)
#> function (x) 
#> rev(x)
#> <environment: 0x55e4936de390>
method(bizarro, class = class_factor)
#> <S7_method> method(bizarro, new_S3_class("factor"))
#> function (x) 
#> {
#>     levels(x) <- rev(levels(x))
#>     x
#> }
#> <environment: 0x55e4936de390>

# errors if method not found
try(method(bizarro, class = class_data.frame))
#> Error : Can't find method for `bizarro(S3<data.frame>)`.
try(method(bizarro, object = "x"))
#> Error : Can't find method for `bizarro(<character>)`.