Generics in other packages

You need an explicit external generic when you want to provide methods for a generic (S3, S4, or S7) that is defined in another package, and you don't want to take a hard dependency on that package.

The easiest way to provide methods for generics in other packages is import the generic into your NAMESPACE. This, however, creates a hard dependency, and sometimes you want a soft dependency, only registering the method if the package is already installed. new_external_generic() allows you to provide the minimal needed information about a generic so that methods can be registered at run time, as needed, using methods_register().

Note that in tests, you'll need to explicitly call the generic from the external package with pkg::generic().

Usage

new_external_generic(package, name, dispatch_args, version = NULL)

Arguments

package

Package the generic is defined in.

name

Name of generic, as a string.

dispatch_args

Character vector giving arguments used for dispatch.

version

An optional version the package must meet for the method to be registered.

Value

An S7 external generic, i.e. a list with class S7_external_generic.

Examples

MyClass <- new_class("MyClass")

your_generic <- new_external_generic("stats", "median", "x")
method(your_generic, MyClass) <- function(x) "Hi!"