A generic defines the interface of a function. Once you have created a
generic with new_generic(), you provide implementations for specific
signatures by registering methods with method<-.
The goal is for method<- to be the single function you need when working
with S7 generics or S7 classes. This means that as well as registering
methods for S7 classes on S7 generics, you can also register methods for
S7 classes on S3 or S4 generics, and S3 or S4 classes on S7 generics.
But this is not a general method registration function: at least one of
generic and signature needs to be from S7.
Note that if you are writing a package, you must call methods_register()
in your .onLoad. This ensures that all methods are dynamically registered
when needed.
Usage
method(generic, signature) <- valueArguments
- generic
A generic function, i.e. an S7 generic, an external generic, an S3 generic, or an S4 generic.
- signature
A method signature.
For S7 generics that use single dispatch, this must be one of the following:
An S7 class (created by
new_class()).An S7 union (created by
new_union()).An S3 class (created by
new_S3_class()).An S4 class (created by
methods::getClass()ormethods::new()).A base type like class_logical, class_integer, or class_numeric.
A special type like class_missing or class_any.
For S7 generics that use multiple dispatch, this must be a list of any of the above types.
For S3 generics, this must be a single S7 class.
For S4 generics, this must either be an S7 class, or a list that includes at least one S7 class.
- value
A function that implements the generic specification for the given
signature.
Examples
# Create a generic
bizarro <- new_generic("bizarro", "x")
# Register some methods
method(bizarro, class_numeric) <- function(x) rev(x)
method(bizarro, new_S3_class("data.frame")) <- function(x) {
x[] <- lapply(x, bizarro)
rev(x)
}
# Using a generic calls the methods automatically
bizarro(head(mtcars))
#> carb gear am vs qsec wt drat hp disp cyl mpg
#> Mazda RX4 1 3 0 1 20.22 3.460 2.76 105 225 6 18.1
#> Mazda RX4 Wag 2 3 0 0 17.02 3.440 3.15 175 360 8 18.7
#> Datsun 710 1 3 0 1 19.44 3.215 3.08 110 258 6 21.4
#> Hornet 4 Drive 1 4 1 1 18.61 2.320 3.85 93 108 4 22.8
#> Hornet Sportabout 4 4 1 0 17.02 2.875 3.90 110 160 6 21.0
#> Valiant 4 4 1 0 16.46 2.620 3.90 110 160 6 21.0