utils (version 3.5.2)

methods: List Methods for S3 Generic Functions or Classes

Description

List all available methods for a S3 and S4 generic function, or all methods for an S3 or S4 class.

Usage

methods(generic.function, class)
.S3methods(generic.function, class, envir=parent.frame())
# S3 method for MethodsFunction
print(x, byclass = attr(x, "byclass"), …)

Arguments

generic.function

a generic function, or a character string naming a generic function.

class

a symbol or character string naming a class: only used if generic.function is not supplied.

envir

the environment in which to look for the definition of the generic function, when the generic function is passed as a character string.

x

typically the result of methods(..), an R object of class "MethodsFunction", see ‘Value’ below.

byclass

an optional logical allowing to override the "byclass" attribute determining how the result is printed, see ‘Details’.

…

potentially further arguments passed to and from methods; unused currently.

Value

An object of class "MethodsFunction", a character vector of method names with "byclass" and "info" attributes. The "byclass" attribute is a logical indicating if the results were obtained with argument class defined. The "info" attribute is a data frame with columns:

generic

character vector of the names of the generic.

visible

logical(), is the method exported from the namespace of the package in which it is defined?

isS4

logical(), true when the method is an S4 method.

from

a factor, the location or package name where the method was found.

Details

methods() finds S3 and S4 methods associated with either the generic.function or class argument. Methods are found in all packages on the current search() path. .S3methods() finds only S3 methods, .S4methods() finds only only S4 methods.

When invoked with the generic.function argument, the "byclass" attribute (see Details) is FALSE, and the print method by default displays the signatures (full names) of S3 and S4 methods. S3 methods are printed by pasting the generic function and class together, separated by a ‘.’, as generic.class. The S3 method name is followed by an asterisk * if the method definition is not exported from the package namespace in which the method is defined. S4 method signatures are printed as generic,class-method; S4 allows for multiple dispatch, so there may be several classes in the signature generic,A,B-method.

When invoked with the class argument, "byclass" is TRUE, and the print method by default displays the names of the generic functions associated with the class, generic.

The source code for all functions is available. For S3 functions exported from the namespace, enter the method at the command line as generic.class. For S3 functions not exported from the namespace, see getAnywhere or getS3method. For S4 methods, see getMethod.

Help is available for each method, in addition to each generic. For interactive help, use the documentation shortcut ? with the name of the generic and tab completion, ?"generic<tab>" to select the method for which help is desired.

The S3 functions listed are those which are named like methods and may not actually be methods (known exceptions are discarded in the code).

References

Chambers, J. M. (1992) Classes and methods: object-oriented programming in S. Appendix A of Statistical Models in S eds J. M. Chambers and T. J. Hastie, Wadsworth & Brooks/Cole.

See Also

S3Methods, class, getS3method.

For S4, getMethod, showMethods, Introduction or Methods_Details.

Examples

# NOT RUN {
require(stats)

methods(summary)
methods(class = "aov")    # S3 class
## The same, with more details and more difficult to read:
print(methods(class = "aov"), byclass=FALSE)
methods("[[")             # uses C-internal dispatching
methods("$")
methods("$<-")            # replacement function
methods("+")              # binary operator
methods("Math")           # group generic
require(graphics)
methods("axis")           # looks like a generic, but is not

if(require(Matrix)) {
print(methods(class = "Matrix"))  # S4 class
m <- methods("dim")       # S3 and S4 methods
print(m)
print(attr(m, "info"))    # more extensive information

## --> help(showMethods) for related examples
}
# }