The R Project SVN R

% File src/library/utils/man/methods.Rd

% Part of the R package, https://www.R-project.org

% Copyright 1995-2015 R Core Team

% Distributed under GPL 2 or later

\name{methods}

\title{List Methods for S3 Generic Functions or Classes}

\alias{.S3methods}

\alias{methods}

\alias{print.MethodsFunction}

\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())

\S3method{print}{MethodsFunction}(x, byclass = attr(x, "byclass"), \dots)

}

\arguments{

  \item{generic.function}{a generic function, or a character string naming a

    generic function.}

  \item{class}{a symbol or character string naming a class: only used if

    \code{generic.function} is not supplied.}

  \item{envir}{the environment in which to look for the definition of

    the generic function, when the generic function is passed as a

    character string.}

  \item{x}{typically the result of \code{methods(..)}, an \R object of % S3

    class \code{"MethodsFunction"}, see \sQuote{Value} below.}

  \item{byclass}{an optional \code{\link{logical}} allowing to override

    the \code{"byclass"} attribute determining how the result is

    printed, see \sQuote{Details}.}

  \item{\dots}{potentially further arguments passed to and from methods;

    unused currently.}

}

\details{

  \code{methods()} finds S3 and S4 methods associated with either the

  \code{generic.function} or \code{class} argument.  Methods are found in

  all packages on the current \code{search()} path.  \code{.S3methods()}

  finds only S3 methods, \code{.S4methods()} finds only only S4 methods.

  When invoked with the \code{generic.function} argument, the

  \code{"byclass"} attribute (see Details) is \code{FALSE}, and the

  \code{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 \sQuote{.}, as

  \code{generic.class}.  The S3 method name is followed by an asterisk

  \code{*} if the method definition is not exported from the package

  namespace in which the method is defined.  S4 method signatures are

  printed as \code{generic,class-method}; S4 allows for multiple

  dispatch, so there may be several classes in the signature

  \code{generic,A,B-method}.

  When invoked with the \code{class} argument, \code{"byclass"} is

  \code{TRUE}, and the \code{print} method by default displays the names

  of the generic functions associated with the class, \code{generic}.

  The source code for all functions is available.  For S3 functions

  exported from the namespace, enter the method at the command line as

  \code{generic.class}.  For S3 functions not exported from the

  namespace, see \code{getAnywhere} or \code{getS3method}.  For S4

  methods, see \code{getMethod}.

  Help is available for each method, in addition to each generic.  For

  interactive help, use the documentation shortcut \code{?} with the

  name of the generic and tab completion, \code{?"generic<tab>"} to

  select the method for which help is desired.

  The S3 functions listed are those which \emph{are named like methods}

  and may not actually be methods (known exceptions are discarded in the

  code).

}

\value{

  An object of class \code{"MethodsFunction"}, a character vector of

  method names with \code{"byclass"} and \code{"info"} attributes.  The

  \code{"byclass"} attribute is a \code{\link{logical}} indicating if

  the results were obtained with argument \code{class}

  defined.  The \code{"info"} attribute is a data frame with columns:

  \describe{

    \item{generic}{\code{\link{character}} vector of the names of the generic.}

    \item{visible}{logical(), is the method exported from the namespace

      of the package in which it is defined?}

    \item{isS4}{logical(), true when the method is an S4 method.}

    \item{from}{a \code{\link{factor}}, the location or package name

      where the method was found.}

  }

}

\note{

  The original \code{methods} function was written by Martin Maechler.

}

\seealso{

  \code{\link{S3Methods}}, \code{\link{class}}, \code{\link{getS3method}}.

  For S4, \code{\link{getMethod}}, \code{\link{showMethods}},

  \link[methods]{Introduction} or \code{\link{Methods_Details}}.

}

\references{

  Chambers, J. M. (1992)

  \emph{Classes and methods: object-oriented programming in S.}

  Appendix A of \emph{Statistical Models in S}

  eds J. M. Chambers and T. J. Hastie, Wadsworth & Brooks/Cole.

}

\examples{

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

}

}

\keyword{methods}