The R Project SVN R

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

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

% Copyright 1995-2007 R Core Team

% Distributed under GPL 2 or later

\name{methods}

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

\alias{methods}

\alias{print.MethodsFunction}

\description{

  List all available methods for an S3 generic function, or all

  methods for a class.

}

\usage{

methods(generic.function, class)

}

\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.}

}

\value{

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

  character vector of function names with an \code{"info"} attribute.

  There is a \code{print} method which marks with an asterisk any

  methods which are not visible: such functions can be examined by

  \code{\link{getS3method}} or \code{\link{getAnywhere}}.

  The \code{"info"} attribute is a data frame, currently with a

  logical column, \code{visible} and a factor column \code{from}

  (indicating where the methods were found).

}

\details{

  Function \code{methods} can be used to find out about the methods for

  a particular generic function or class.  The functions listed are those

  which \emph{are named like methods} and may not actually be methods

  (known exceptions are discarded in the code).  Note that the listed

  methods may not be user-visible objects, but often help will be

  available for them.

  If \code{class} is used, we check that a matching generic can be found

  for each user-visible object named.  If \code{generic.function} is

  given, there is a warning if it appears not to be a generic function.

  (The check for being generic used can be fooled.)

}

\note{

  This scheme is called \emph{S3} (S version 3).  For new projects,

  it is recommended to use the more flexible and robust \emph{S4} scheme

  provided in the \pkg{methods} package.  Functions can have both S3

  and S4 methods, and function \code{\link{showMethods}} will

  list the S4 methods (possibly none).

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

}

\seealso{

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

  For S4, \code{\link{showMethods}}, \code{\link{Methods}}.

}

\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")

methods("[[")    # uses C-internal dispatching

methods("$")

methods("$<-")   # replacement function

methods("+")     # binary operator

methods("Math")  # group generic

require(graphics)

methods("axis")  # looks like it has methods, but not generic

\dontrun{

methods(print)   # over 100

}

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

}

\keyword{methods}